MR_SLINMy guess is that they don't need to move quicker. The game has lasted this long with only a few major patches each year, and the people who play TF2 as such diehard fans that they can avoid patching the game for MONTHS and the game still won't die. In addition, they can experiment with random things like mann vs machine, contracts, and killing off community servers with matchmaking and the game STILL won't die. My best guess is that they can afford to wait.
Competitive players have waited long enough. Hell, it hasn't even been three years since I first started playing tf2 and I'm getting to the point where it just isn't worth it for me to spend time getting good at a game where the higher level players all leave every year and there are no actual tournaments to speak of. I dislike the casual aspects of overwatch but at least there's a chance that I could get some actual competition where people don't spout shit like 'oh we don't scrim much/are offclassing/don't care about the game' whenever they lose if I switch over.
The competitive scene is dying because of overwatch, and the casual scene is dying because valve is trying to make the game competitive. By the time they finish testing all their stupid ideas regarding matchmaking and either come up with our format or a shittier one where the casuals can play perma spy, they'll have no players anyway.
You're right in that the only chance we have is in TF3 but that's going to take even longer than a fixed matchmaking system and might never happen (also like a fixed matchmaking system) so it's getting to the point where it doesn't really make sense for anyone to keep wasting their time on this game anymore.
I'm pretty sure clockwork cares a lot more about this game than most people and even he's gone to play overwatch because it just doesn't make sense not to, even if it is a much worse game in many respects.