castling
For decades there haven't been any engines that play at a level of, for example, 1200 or 1300.
So to make engines at a 3000 level play so much lower, they have to do some odd things. They can limit things like search depth and thinking time.
Castling is a strategic type of move. It improves the position for the future. An engine that thinks for a fraction of a second or only 1-2 moves deep may not ever castle.
This is one reason human opponents are better i.e. engines play artificially and are generally poor strategically. They've beaten humans for decades because their short term tactics are basically flawless, not because they make good long term moves.
There are cases where castling is bad because it's done too early, or castling is just wrong altogether, but 9 times out of 10 it's better to castle, and a player is much more likely to castle too late than too early.
Particularly in 1.e4 e5 games and 1.d4 d5 games, the center is liable to open quickly, so it's very important to castle quickly.