When a complete newcomer comes to a field and sees professionals not doing a simple thing, the right question isn't "why don't you just do this, duh", but "I thought this would work, why doesn't it?".
I'm not a newcomer though, I've worked on both cheats and anti-cheats going back more than two decades. I know how the sausage is made and it's not pretty.
The anti-cheat companies you talk about mostly sell a mass produced product that works very similarly to anti-virus software. Games embed the anti-cheat module and its cheat definitions get updated. Statistical analysis requries both knowledge of the specific game and access to its database. Often also additional game programming to even store the crucial data. A bespoke solution. This can't be mass produced and is expensive, so most games don't have it.
So to bring it back to the newcomer question, I thought this would work, why doesn't it?, the answer is that game companies don't want to spend the money. [1] A classic answer to most annoyances in life, really.
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[1] An interesting outlier is the online gambling industry, especially online poker. They spend way more money than non-gambling game developers and have much more sophisticated anti-cheat systems, including statistical analysis. It's also fun to see how techniques used to get around online poker anti-cheat detection slowly make their way into mainstream gaming with a delay of about 15 years or so. As a simple example, nobody serious was even running their code on the same system as the game client back in 2005, instead parsing the video signal and simulating HID inputs. [2] Took more than a decade to see popular cheats for regular games go to that length to avoid detection. Not because the cheat developers were less capable, but because the anti-cheats didn't warrant the investment.
[2] Thus taking the battle almost completely to the statistical analysis realm. Are your mouse movements random enough, with good jitter? Does your bot take belivable micro breaks? Does your average performance, including reaction times, degrade at the end of a long session as you get more tired? Et cetera.
Many cheaters were already trying to not be obvious, most I've encountered playing various fps games are not the typical spinbot in csgo. Instead they might play with only wallhack, aimtrigger, or even no hack, and only turn on the big hacks halfway through a game if they're not winning or think someone on the other team is hacking as well. In some games they use bots to dunk their stats when not playing.
AI detection is also coming to videogames with anybrain.gg, but seems like these can be countered with AI enhanced cheats no?
As an experienced player with an anti cheat/cheating/security interest it doesn't seem like statistics is the silver bullet you claim it to be, at least as your only detection/protection. It combined with normal protection/detection methods is likely what Riot is doing.
I'm definitely not advocating for doing less to counter cheaters. I'm just talking about how more could be done. As in, continue with existing methods and add new ones.
Also, yeah many cheaters would start being more conservative and manage to evade detection. However that is also a win. It's the aggressive obvious cheaters that are the worst, because it makes it obvious that the fight was unfair. If the cheater made it look plausibly legit, then the victim won't feel as bad.
