Why has Valve not fixed anything?

Why has valve not decided to fix any of the long issues us players have been dealing with in the recent years? Such as their horrible anti cheat which actually doesn't help anything at all... If they were to use Easy anti-cheat, we know for sure that the amount of cheaters would actually go down. So why have they been waiting out on fixing this?

Source Engine 2.
Laziness
Take a pick and what you'd prefer.