We're old, grouchy, and have lives now hence the death of the internet we knew and loved.
Facebook, Twitter, Instagram, Reddit, Twitch, etc. have become the dominate reason to be online now-a-days. The internet went from being small groups of nerds/geeks gathering to talk about their favorite video games/anime/etc. on little know forums/sites to being a full blown social experience now with everyone tweeting about what they do during the day, posting new selfies/pictures on Instagram, stalking that crush from high school or connecting with an old friend on Facebook, theorycrafting and running numbers on Game Sub-reddits, etc.
The old school communities are dying out pretty much for all the reasons you mentioned. I'd love to see those days come back but considering I'm now 30 and have a full-time job that leaves me exhausted at the end of the day I just don't have the time like I did 16 years ago when I was a Freshmen in High School that just got his first computer. Hell I barely have time to play video games, watch anime, or go out drinking anymore. The internet we helped to bring into the mainstream has evolved into what the new generations want and need. Sadly it's either get with the times or reminisce about the old days on forums like AC that refuse to give up what the internet used to be (and sadly there are only a few of us that still do that. DX, Sledge, myself, and Myk are pretty much the only active members on AC anymore).