Why do so many people cheat on this app?

https://support.chess.com/article/648-what-do-i-need-to-know-about-fair-play-on-chess-com
https://www.chess.com/article/view/online-chess-cheating
If you feel any of your opponents or other members are using disallowed resources, you should report them. The site has a dedicated team to handle fair play and closes tens of thousands of accounts each month.
https://www.chess.com/article/view/chesscom-update-october-2023#FairPlay
That, said, discussions of cheating, potential cheating, or cheat detection are not allowed in the general forums.
If you would like to discuss join the following club. https://www.chess.com/club/cheating-forum