Honest question: given all the companies and people working on anti-cheat systems for the last 20+ years of multiplayer video games, don't you think it would all be server-side if it could be, by now?
No, because most companies will make decisions based on time/effort/profitability, and because client-side anticheat is stupid simple and cheap, that's what they go with. Why waste their own server resources, when they can waste the user's?
No, game companies are simply unwilling to pay for the talent and man hours that it takes to police their games for cheaters. Even when they are scanning your memory and filesystem they don't catch people running the latest rented cheat software.