Valve essentially killed off community servers with their big matchmaking update in Team Fortress 2 and made it near-impossible to find a populated Special Delivery match, so I quit playing.
Yup, second this. I don't understand the posts about the F2P update, as I think TF2's best days were probably in the years following the F2P decision. But the matchmaking update seemed to go out of its ways to kill community servers and a bunch of the less popular game modes, in order to funnel everyone into the more "standard" modes and maps that would be used in ranked. I always thought competitive TF2 deserved more love, so I was cautiously optimistic at first, but the ranked queue times were insane and nobody wanted to play that rule set - it was too little too late. So the ranked mode died, and after that the devs apparently decided to abandon the game completely. Now the official Valve servers (basically the only place to easily find games anymore) are full of nothing but hackers and cheaters. They killed off the community of that game for no reason. It's sad.
Rainbow 6 siege.
Removed secure area, removed some of my favourite maps from ranked.
This too. I couldn't point to a specific update that made me lose interest in Siege, but the trend for that game has been less about adding cool new content, and more of a Ship of Theseus situation, where they've slowly replaced the old Siege game I enjoyed with this strange shadow that I barely recognize.
Some old maps I enjoyed have been removed from all public playlists (and apparently even private matches at this point, but I haven't played in a while to verify). Many others have been "redesigned" in a way that consistently comes out feeling bland and lifeless afterwards, a pattern that has carried over into most of their brand new maps as well. They also removed the ability to play night versions of maps, removing variety on the few maps left I still enjoy. The last few times I've logged on, it felt like there was maybe a 25% chance of me playing on a map I actually enjoy. I don't know if the map designers changed or what, but the designs have felt like they've been going consistently downhill since sometime near the end of season 2.
The Devs at Ubisoft recognized a fundamental issue with the engine for their game that limited their ability to add new content, but intead of taking the opportunity to start from scratch and release a sequel built on a solid foundation, they instead opted to just slowly overwrite the existing game until a new one emerged, which makes it impossible for me to go back and play the game in the way I used to really enjoy.
They're apparently about to start doing the same thing with Operators too - adding fewer new ones in favor of "reworking" the old ones. Based on the mechanics on the new operators they've added over the past few seasons, I don't have much faith that these reworked characters will turn out any better than the reworked maps.
A pro might say the game is more balanced now, I'm not sure, but it definitely feels a lot less fun for me to play.
It's going to be weird looking back in 10 years, knowing that so many of the experiences I've really enjoyed with my friends can never be recreated, because the game we connected through no longer exists anywhere. It's a major downside of these service-style multiplayer games that we've all kind of just accepted as a necesarry evil to keep content flowing and the meta interesting.