2-it saves you time
Why do grandmasters and others higher rated players resign and not play till checkmate these days?

A better question is why do average to low-rated players resign?
Grandmasters playing other grandmasters know there's a 99.999% chance they'll lose anyway if they continue to play, so resigning makes perfect sense.
Whereas with average and low-rated players in a losing position, there's a realistic chance their opponent will blunder a piece or let stalemate happen or be unable to convert a material advantage into checkmate in the endgame (e.g. king and rook is a theoretical win vs king and knight, but the player with the rook might not know how to overcome the knight's defenses before the 50-move rule kicks in or time runs out).
But it still makes sense for average and low-rated players to resign in OTB tournaments when they have more games left to play, to save their time and energy for the remaining game(s).
I have noticed that everyone prefers resigning than playing till the very last move unless your opponent is low on time. But why is it done? What’s the problem of being checkmated on the board? After all, you anyway won’t win after resigning!
Resigning a game is nothing new. Mic drop!