It's called getting older. When you're in high school most, if not all, of your friends play video games regularly. Once you hit college, many of them stop. Once they graduate college and get jobs, even more stop. Once they get married, even more stop. Once they have kids, even more stop. Ultimately there are far fewer players from your generation who are left to play with you. Naturally the community is going to feel different when the majority of the players don't like the same music you do, didn't watch the same movies you did, and don't face the same problems you do.
You can huff the copium and chalk the changes up to made up concepts like "toxic positivity," but the fact is that the internet has brought many elements of society that previously had no contact with each other together. The "dirty jokes" and the disparaging remarks that used to seem funny to your buddies are not as funny when they're at the expense of people whose company you now regularly enjoy. I, for one, prefer "toxic positivity" to the mean-spirited community that I grew up in and to the elitist jerks who design WoW. I don't have to be mad at my fellow players all the time to enjoy my video games.
The fact is that Brian finally acquired the perspective to recognize that there is far more to life than playing video games. Good for him. Someday his kids will be older, and he'll find himself with free time again. He even explicitly said that when that happens he'll likely come back. Most of us will likely have moved on to bigger and better things by then, but I'm sure that many of us will still be around to welcome him back with open arms.