The only reason we had a free internet in the first place was because we had free computers. Many people no longer have free computers.
It's not just the App Stores that are at fault here, almost unbeatable screen time[1] protections, limited mobile APIs, battery usage optimizations and carrier-grade NATs also matter here.
Hosting video is extremely expensive. Either you fund it with ads, which is hard for porn, with subscriptions, which is impossible because of Visa/Mastercard rules, with cryptocurrencies, which are easy to ban as per above, or you offload the cost to P2P, but smartphones are effectively barred from participating in P2P networks due to the above reasons.
This is also a major driver behind the fall of piracy. Piracy is easy if everybody has an always-on device with a stable internet connection and a good power source. This is no longer the case.
[1] By "Screen Time" I mean Apple's comprehensive suite of tools for device access restrictions, both for owners and children. These restrictions don't just concern screen time, they may also prohibit certain apps (or categories of apps) entirely. The point is not restricted to Apple, similar solutions exist for Android, and they give even more power to the parents due to the system's open nature.
