They don't do anything because they don't need to, the game is fine as it is. The only thing they can do is polish the gameplay a little, which they are doing step by step, the last time they were doing fast changes there were a huge backstab from the community, mainly from the rework of the pistols and rifles, which they had to change back. Now they are adding things time by time, testing, analyzing, it's all they can do really.
Ofc when you play a game for 15k it will get boring, it's impressive csgo even took that long for you, most games get boring before you play 50 hours. But csgo will never die, because there will always be new players coming into the game, and because it's multiplayer it's a game that'll never end, it's simple, fair, and every match is different, there will always be something to learn when playing one cs match. If developers kept adding things to the game, it would get too complicated, and the game would be like lol, there is always something new but there will be a time when it's just too much, and new players would be more likely to give up.
As for the anti cheat part, I'm sure they're working on it, people think making anti cheats is as easy as gaben saying ''guys upgrade the anti cheat right now'', when in reality it's very complicated and it takes time to do. Valve already said anti cheat is one of their main goals,
For the 64 tick part, there is a considerable amount of players that can't run 128 tick, myself included. Valve wants as many people as possible to play the game, that's why the graphics are simple and the game is cheap. If they were to update the tick in MM they would lose a fraction of their playerbase. If you can afford a PC that runs 128 tick, you can as sure as hell afford to pay esea or faceit.