I'm pretty sure it's a combination of two things:

1. Social media, allowing outcasts to form their own dysfunctional online communities;
2. Easy access to porn through smartphones, allowing people's porn addictions to fester.

Both are a result of smartphones, in a way. Smartphones massively increased overall internet use, because they're cheaper and easier to use than computers (app interfaces are so easy, even the semi-literate can navigate them), so more people were able to get online. And because of this, both access to and use of internet porn increased massively after 2007. Remember, even in the mid-2000s, if you were a porn addict you were usually a porn theater goer or a collector of VHS tapes and DVDs, which took a lot more effort. The introduction of smartphones changed the game on that and led hundreds of millions of people to quantities and types of porn that they otherwise wouldn't have looked for.

Look, I drew a diagram of what I think happened.