Kind of difficult to figure out what happened. I'm a little on the younger side than most people in this thread but I do remember a time when the internet was mostly a nerd thing and when memes actually died. I think it's mostly the internet going mainstream that has caused this massive shift in culture. Before it was just nerds doing dumb things, sharing stories and creations, and was small but somewhat purposeful. Hostilities were way lower, and everyone was just a screen name.

Now look at what has happened. You have to attach all of your personal info to everything, most content is shallow for the purpose of pandering to the lowest common denominator, and people attention whore despite not actually doing anything of value. Also, because people have to know absolutely everything about each other, politics have become intertwined in places that they really don't belong. It's gotten to the point where people's politics determines the sites they go to, even if the site isn't inherently political. Are you far left? Tumblr, Twitter, Facebook. Do you dislike the far left? Reddit, 4chan. It's gotten so bad that people outright refuse to go to places because "there are too many of X people that have different political views than me". But you're just going to a place to look at art, shitpost, and maybe get porn, who cares about people's politics? Yet it has become integral. People's politics define them.

Thanks to the social justice people of the far left pushing so hard to sterilize everything and make it as inoffensive to their noble sensibilities as possible, they have bred a counter-movement that tries to make everything as hostile and offensive as possible. Whereas years ago hostility was a mere possibility, now it's a guarantee. Many popular youtube channels exemplify this, with their humor stemming from being as irreverent and offensive as possible.

Furthermore, the mainstream audience is much more shallow than the nerd audience was. While the internet was certainly a place for dumb random humor, that has been amplified and combined with people's cripplingly low attention span. You can see this with sites like Vine and Twitter, where the purpose is to make short, random, "relatable" quips in 6 seconds/150 characters.

Combine all of this and you get the shallow, hostile internet we have today.

The question is what can be done. The biggest problem is that before, everyone knew where to go. Even if new sites or networks were made or used, who would know to find them?