Making a 'true anticheat' isn't really that easy, as a lot of methods used to cheat nowadays, which makes it much much harder to pick up on.
To detect something, you'll have to figure out what they're using, if you patch it, they simply find another way to do it, a cat and mouse game is pretty much what it boils down to.
A lot of data analysis is done to battle cheaters as well, this includes statistics as well, so if it's suspicious, it typically gets flagged in most games.
This can also be done with the help of AI, for certain cheats such as those that get rid of recoil and aimbot could be detected, though it won't be perfect either and might also cause their own fair share of false bans. I know there has been a lot of development for AI Anticheats, saw a lot of talk regarding this a long time ago, though I suppose it wasn't that great as it fell off.
It likely takes a lot of data and time to train it properly for a specific game as well, which could take more time and resources than it's worth it, so it might be better using more direct detection systems.
As for IP Bans, they are typically always enforced for most games, but they aren't useful nowadays anymore as users have dynamic IP addresses, which means that their IP address can change, making it functionally useless.
There are of course other methods that are implemented to prevent users from making new accounts, but anything can be bypassed if they just have enough time to find out how it works.
The fact that this is an issue affecting the entire industry, filled with experienced anti-cheat developers, is an indication that this isn't a simple issue to resolve.
Typical quick resolutions would be to add paywalls, require more authentication (Phone numbers, ID, e.t.c.) and stuff like that, but this also restricts the normal playerbase and can cause a lot of backlash.
If it were a closed system like a Playstation, then it would of course not be much of an issue, but since these are open platforms anyone could use, it pretty much levels the playing field for cheat devs and anticheat developers, in most cases tipping in favor more towards cheat developers.
To detect certain things you would have to be extremely intrusive, in most cases completely unnecessary and achievable in other ways.
The situation sucks, I've seen so many cheaters in so many different games, though games aren't keeping these cheaters in their games because they want to.
It's of course quite easy to say to 'just fix it', but these things are typically really deep rabbit holes that cannot simply be fixed by working harder.