Those things have nothing to do with containerization. They can do those things without it. Containerization exists to improve privacy and security. It can do the same thing on Linux.
Even if you trust an app, it can have vulnerabilities you are unaware of. Containerization helps limit the effects damage from a vulnerability could have. They also simplify the distribution of software, which is the primary goal of Flatpak. There are benefits for using containers for open source software, you're just refusing to acknowledge them. Nobody is forcing you to use containerization, and I don't care to convince you to. I just think acting like Flatpak and other container based package formats is some corporate conspiracy is silly. Flatpak is FOSS and mainly distributes FOSS.