Why do many people not know Knight and bishop mate?

@tpr I once had a training session with Karl Heinz Podzielny (known as Potz Blitz among german players, 2500 strong IM) for a coffee per try, he did it in 20 secs, but stiff drunk. Maybe sober he would have been faster ;-)

I can do knight and bishop<depends on the place>in 17 moves

I've seen womenGM on a official game drawing(or losing) because she did not know how to mate with bishop and knight :P but I cant remember the game to post a link (as far as I remember she wasnt like completely disoriented or something she just did not know how to do it and analyzed it real time which cost her time and effort and either she lost on time or she drew because of the 50 move rule cant remember exactly what happened maybe she offered a draw after trying unsuccessfully to mate? )

So that should be enough to tell you that you can go far deep in chess without the need to memorize it :P

It is basic knowledge. In the blitz game mentioned above, my friend was in a losing endgame, but he found a way to sacrifice his two pieces for the last two pawns, thinking it would be a draw given the little remaining time. He was mistaken, of course Tigran V. Petrosian could do it. Now imagine something like that in a long game: say you are winning and you end up KBN vs. K and you cannot checkmate in under 50 mobes. What an embarassment. I have seen that happen in a tournament.

Compared to other things it is pretty easy indeed.

@Chess-And-Tech no, you can't

in a specific position there is also 1 move @Botchwinnik

@Chess-And-Tech that isn't the point.

There was this 2400 player in the marathon, who had bishop and a knight and could checkmate me. He had to accept a stalemate lol.

An embarrasement is not knowing king and pawn opposition
for top players.