Most of those SaaS have native mobile apps which track you, too. The runtime is not to blame. FOSS applications could be delivered with near-instant load times, native feel and excellent sandboxing, with one universal build target.

That is a remarkable ability.

Do not let the crimes of Web 3.0 blind you to this.

Tracking and disrespect for privacy are utterly orthogonal.

Native can track, Web always does.

Almost no one needs to develop a self hosted app, because there already are self-hosted apps for lots of use cases out there.

Such as?

I was going to list some use cases individually, but you can get a better picture by skimming through this: https://github.com/awesome-selfhosted/awesome-selfhosted

It's rare that a self-hosted piece of software is not present on this list. As you can see, the coverage is pretty extensive.

Nice list, and what is the market share of them?

There are things like Minio which lots and lots of people use as an S3-compatible object store because it's so simple to set up. Most S3 alternatives are just a part of much larger filing system that's more demanding to set up. NextCloud is pretty big as well, though I don't know the exact numbers.

I think in the end, it doesn't matter as much. These are meant to be deployed for a cohesive user base that numbers between a single geek and an entire region of a country or small org.

They most often use libre data formats and protocols to store and communicate data. In such a situation, the network effect is less pronounced, and measuring market share isn't as important. As long as the service works reliably and meets user needs, I don't think people will clamour to replace them with proprietary solutions.