Multiplayer games offer a neverending challenge. There’s always a better opponent.

But that is exactly the problem with it. The vast majority of people don't have the free time to spend on a given game to compete with those who do spend most of their time on it.

Maybe I'm doing it wrong or I'm just too shy to socialize with strangers in these games, but as someone who has fond memories of my favorite TF2/killing floor community servers, I feel like there is basically no sense of community in these games now that matchmaking is king and private hosting is a thing of the past

Never been a multiplayer fan, reading the above its the same story as many other hobbies and recreations tho right?

offer a neverending challenge

....which requires continuous ongoing investment to overcome or even compete

There's always a better opponent

...who has more time or resource to put into getting better

And I've made a lot of good friends through these communities.

...because they attract similar minded people, but there's also toxic dickheads as well

I feel like the good bits and the bad hits of community are the community

Ya need to play more grand strategy games and CRPGs. Theres plenty to sink your teeth into such as eugenics and war crimes, im thinking specifically Crusader kings and Tyranny with these two examples.