Flatpak is completely open source software and any proprietary software in it has a large warning about how it's proprietary. I don't know why you think proprietary software vendors are pushing these. Ublue, NixOS, and Fedora Silverblue are all community run, not being pushed by some malicious group pushing proprietary software.
Why companies even have anything to gain from their proprietary software being in a container? All that would do is make data collection more difficult.