The idea of cheating in general is like a game of cat and mouse.
The cheaters constantly evolve their cheats to bypass detection by anti-cheats.
The games try to constantly update their anti-cheat to catch those new cheats.
Since TF2's anticheat isn't being updated, literally any kind of cheat made nowadays would work.
Community servers, on the other hand, use a custom anti-cheat along with the standard VAC one. All I can say is that we're doing our best to update our anti-cheat to catch the newest cheat methods, but with the limited access we have (we can't go too deep into the player's PC like a regular anti-cheat can) it's proving rather difficult. There's a reason why some servers like FaceIT force you to install an anti-cheat client on your PC, it's to grant them those permissions to make a better and more effective anti-cheat.
Back to the main question - I think there are so many cheaters in casual, that they're "overflowing" more into community servers recently. Lots of cheats are basic and easily caught, but it seems like they're finding new ways to bypass the anti-cheat.
You can see our sourcebans page to see just how many people the anti-cheat catches without you actually knowing. (Also,
@Bigunit being a chad and going ham catching cheaters from calladmin reports, good job mate)
I also think this is the so-called "negativity bias" of humans, where you don't notice something until it's bad or annoying (Like you don't notice good audio in a video, you only notice bad audio in a video)