Just look at Minecraft which was made in 2009 that uses Java. I could easily be talking out of my ass, but there are certain things we learn as programmers and that is modularity and maintenance, and frankly an older anticheat would in my eyes require exponentially more maintenance just based on the original architecture it was built on. The problem is keeping up with new cheats and every time there is a new type of cheat not based on old methods of cheating valve needs to manually account for them whereas a new more modern anti cheat would (or should, sorry valorant) be accustomed to most types of cheats. Same goes for VAC, which is an old anti cheat at this point likely also created by millions of lines of code. There's a reason operating systems like Windows have so many inherent flaws (aka viruses and overall security) for example and that is because the incredible amount of possible vulnerabilities available within the 60 million+ lines of code and it's also a result of years of bad design choices.

If you don't understand how a development cycle works don't bother trying to unless you're into coding.

Valorant anti cheat download