Why show half of a story which will never be completed?

A few days ago the UK channel 5 USA showed the final episode which ended of a collossal cliffhanger and then said "That was the last ever episode". Why show this if it will just leave us hanging? If they were really going to show it why not warn us that it introduces a never to be resolved story line and so give us the choice to watch or not to watch?

If the channel had been airing the show as it was being made this might be understandable but only after the event do I and my fellow Freeview viewers learn that it was cancelled FIVE YEARS AGO after series one.

I think this is seriously unfair by thr broadcaster!