I think the figure was that almost half of the traffic on the internet was related to porn sites.

I have no idea if there is any updated stats for that.

I suppose you could surveil a major internet node and check all DNS requests to estimate how much traffic is “porn related” overall.

You most likely do not want to learn about these.

Back in the late 90s, early 2000s, with the spread of the internet and cheap digital camcorders, a lot of amateurs started doing their own niche porn. These were content that most porn studios (who, up to this point, dominated the market, as they were the only ones able to front the cost of equipment, editing, and physical media creation) simply wouldn’t take on, because the content was illegal in certain countries - not talking about truly illegal shit like bestiality or CSAM, but many countries, including e.g. the UK, where anything that is, and I quote verbatim, “is grossly offensive, disgusting, or otherwise of an obscene character”. Now, you can see how such laws can be applied subjectively, and how one could argue that, say, gay porn, or anal, or gangbangs, fall under the umbrella of this terminology.

Anyway, the point is, most studios stuck to their core content of generic porn, while thousands of websites popped up focusing on a niche, or ran by the actor/actress themselves.

Then around 2012-2014, payment card processors began cracking down on porn, due to pressure from certain religious groups… And of course they targeted the small fish, these independent creators, not the big ones like PornHub etc. (btw neato little fact: the top, what, 7-10 porn sites today are all owned by the same company, just like how most dating apps are all owned by a single company too), where a lot of creators went, as they provided the entire hosting, marketing and payment processing service stack, so people just needed to upload the videos and watch the money roll in.

Then we had a slew of services trying to cash in on the adult content creation craze triggered by the pandemic - that’s where OnlyFans, JustForFans and the other similar sites became super popular - and now there’s a constant ebb and flow from and to these platforms. Many are joining to try and find stardom, many are leaving due to the abusive practices and are running their own website, some are spinning up services like these but with lower fees, the list goes on.

However one thing most of these sites don’t take on, is what one would consider “extreme” porn. Let that be fringe fetishes, niche specifics, or truly extreme BDSM. And even with said ebb and flow of users from the hub style sites, the majority of independent porn sites aims to cater for these niche tastes. So unless you wish for a list of sites where people are drinking piss, playing with shit, or where guys are getting their balls, or girls are getting their nipples nailed to boards… No, you probably don’t want to hear about them.

I wonder how they came to it.

Internet pornography or online pornography is any pornography that is accessible over the [Internet primarily via websites FTP connections, peer-to-peer file sharing or Usenet newsgroups.

So I willing to bet the reason to use any other then what you identified is for really nasty shit.