Why was the blood so fakely red?

Remember that this was a STAGE production that was videotaped, and not originally meant to be "filmed," per se. (Note that there's a live audience laughing and applauding throughout.)

I saw this very same production with Lansbury and Hearn in the same theater (the Dorothy Chandler Pavilion,) where this was taped when I was in High School. Same cast, sets, costumes, etc. The theater is HUGE. They used to broadcast the Oscars from this theater before they built the Kodak.

The blood in the show had to be seen from a couple of hundred feet away, as well as from a couple of hundred feet above (3 balconies.)

The "brighter" the shade of red, the better it "reads" from far away on a large stage with an audience of over 3,000.

In the new movie, it's kinda fake red too. I like it, I think it helps with the feeling of the old melodrama. It's doesn't necessarily have to look real. In fact, I wouldn't mind it being even faker-looking.

speaking as a sometime spfx makeup artist, various stage bloods photograph differently. the most vital thing about this particular stage blood was not how real it looked either on camera or on stage, but undoubtedly its ability to be easily cleaned off of the costumes. (most stage bloods stain cloth something fierce!)

Probably so that the audience can see it clearly.