Why do many people not know Knight and bishop mate?

Many people even 2500 do not know knight and bishop mate

Agreed

I will make a video of that in my next youtube video

1) It is quite difficult
2) Since it does not happen every day, it's not worth spending time studying it
3) Personal opinion: it requires more strategy than tactics. New players prefer the latter...very often, i'm playing very stong opponents in middle game, but that have no clues in endings

Its difficult, its rare
Too much advantage

"A beginner should not be allowed to play a game of chess until he can checkmate KBN vs. K" - Capablanca
It is not that difficult
It is fundamental
It does not happen often, but it teaches you how to coordinate B and N, i.e. it teaches you to play chess.
I doubt any 2500 player does not know this. Most can do it in a few seconds.

Umm in real world in 2001 I was playing a titled GM he had a KBNvsK I did not have the knight and bishop he did
But still it was a stalemate so draw!

They don't encounter B+K mates often, so they won't learn it from experience neither will they invest on studying it. As rating points don't measure your skill level in all areas of chess but simply follows from your wins or losses, knowing or not knowing rarely encountered problems won't have much effect on your rating.

@tpr actually some don't, I've seen it myself in a Bundesliga match. If you know the method, you can do it in 20 sec flat, maximum of 35 moves from any given position.

A friend on mine had it in a blitz game against tha late Tigran V. Petrosian. They used an analog clock, but with a needle on the flag with a finer time scale. Petrosian did it in 10 seconds.