Why is this movie ranked so high?

that are objective facts
someone can hardly say something against it.

and though i also like Top-lists, even by those magazines and institutes you have posted,
(cause i like to check and find these essential films i ve still not seen yet)
there IS something to say against it,
because its not so objective as it seems to be.

first of all… you have quoted just british and american sources.
they are quite important, because US-film-industry is important,
but its something which shouldnt be overlooked.

The Archers, which have made this film, are british people
and their films are cult in the UK. absolutely cult!
so its not a big surprise that a film made by the Archers got a very good position in their best of lists.
but their standing is not the same outside of the country.
except maybe in the USA, as we see here, in the lists you have posted.

i am from austria and they have by far not that huge reputation here
and their films were also not that often shown here in TV.
nearly nobody in austria knows even the term "Archers"
(though i can just say that about the 80s till nowadays.
and in those years there was a time in which they have shown us very much old black-&-white films).
(think the same goes with germany.
not to think about eastern asian coutries a.s.o. how well they know old british cinema)

why american critics love this film that much is not so easy to explain.
i have 2 ideas with that:
1) there is something which is called anglo-american-culture
2) american film industry is something specific and so are the critics of this market.

the film industry in the USA is f.ex. different then this in europe.
we have to compare just the Oscar Awards with Cannes,
which films win there and which here.

i dont want to say that one is better than the other,
but the point of view is different.

USA film industry (and its an "industry") is looking for money, the most of the films are entertaining films.
and this film here is in the tradition of entertainment cinema.
so… an entertaining film, even though its from europe, is something american critics are used to review
and english films are even easier for them to review, easier than f.ex. a swedish or an eastern-european.

its a different concept behind it.
its not said that europeans dont make mainstream movies for money, they do!
but even very successfull european mainstream films, f.ex. made by Louis de Funes, who was quite big in Europe, will never have such a good position in a european critics best of lists.

US-best of-Lists are full of old and respected films which where quite progressive that time they were made.
they have done something new for a genre and thats why they have to be mentioned high in those ratings.
its a more historic view on films. if they are still "working" with the audience is not that important.
even if a comedy is not that funny anymore, it is in the list, because in a historic point of view it has to be.
there are some "dated" films in the lists, because they are rated as films of an era and how important they were that time.
and its okay, that it is that way.
i understand that
and i respect that.

in europe we have 2 different point of views on film.
one is the same like it is in the USA.
it is, because the US-american film industry is quite dominant even in europe.
most of the films we see come from there, be it in cinema or in tv.

but there are also some other critics. these are more on the Cannes-side, not so much on the oscar-side.
(i know its black and white painted. i know that there are some east-coast-critics which love european cinema, but on the whole it can be said that way). in their lists you would find a lot of Bergmans, Fellinis, Tarkovskyis and so on…. Their top-lists - if there even exist some - would be and are totally different than those of the USA.
these more artsy films are more like books, not just entertainment, they are - thats the way i think - even more timeless. a bergman film cannot be dated, not really.

and then we have top lists like this one here on imdb.
though we have mostly american, british, and by hollywood-influenced-europeans ("westerners") on this platform,
here are also people from other parts of the world.
the people in general watch films, mostly without a historian view. they are entertained by a film or they are not.
they arent so much influenced by critics, though maybe by commercials, but at the end mostly by their feelings during watching a film.
and this is quite honest and also to respect.
thats also the way i watch a film like "the lady eve".
it has to "work", it has to do what it was intended for
and if it dont do that
it missed the target.
there is no bonus for historical importance.
i rate an Eisenstein-film or an Chaplin-film high, because it still touches me enormous,
though not in an entertaining way,
and i do not rate them high because its an old and important film.

(though it sounds if i didnt like the film, which is not true.
i had fun watching it, it was okay, it was… good!
but it was not such an amazing experience which it has to be to get a 8+ rating by me)

it doesnt mean that people nowadays are not that sensitive anymore.
the people of today are just different.
there is no better, just different.

so!
there are 3 ways
and every way is legitimate.

if you think the movie is amazing then stick on your lists by AFI and so on…
but don't blame the people that they have to rate them higher,
cause AFI says so.
they have a different view on films.
its a more up-to-date view.
the best of list here on imdb is more an extract of the time right now.
(even 1 year later a lot of those films which were in the top 50 will disappear)
that is what the imdb-top-list does
and it is quite interesting in its own way.

AFI and the others above have a maybe more historian view
though of a specific(!!!) culture.
and if you think this is the one right for you, than use these lists and stick to them.

and if you are more interested in world cinema and film as art
there are other lists which are also very different than those listed above,
but not less objective than those made by the american critics.
and in those listings a film like Lady Eve will maybe be considered, because also these lists are somewhat historical, but they are mostly not so much interested in entertaining movies.
so "lady eve" will be in those lists not at the top….

1) "Lady Eve" is a british film, british people will say its one of the best of all time, like "Sami Swoi" is the best film for polish people (though nobody outside knows it)
2) "Lady Eve" is in english so its easier to get reviewed by us-americans
3) its a mainstream-entertainment film, so it got better reviewed in the USA - or even considered because of this fact
4) its a good movie, but not for all film-lovers
5) its an quite old film, times have changed and feelings too.
6) and in the point of view of visual art its not so stunning. its a film which shall entertain, if its not….

so 8.0 is really a high rating for a film of this genre... extraordinary high

I get the impression that you think it should not be rated so highly.