Anticheat Update Tracking

Forgive my ignorance, but why don’t game developers put more effort into limiting the amount of data accessible to the client (restricting it only to what’s reasonably necessary)? For example, couldn’t more movement physics be validated or handled server side? Cheats might still be able to read some data from the game process, but ideally, they’d be limited to issuing inputs like any other player, based only on the same visible output everyone sees. Is it cost? Does this model just not align with how the client/server split looks in games?

You don't want clients suffering a bad experience because they don't have gigabit internet