Flatpak isn’t without its problems, but both front end and back end are open, and one can host his own flatpak repo. Canonical keeps Snap’s back end proprietary, so it is not possible to host your own Snap repo. Canonical being Canonical.

It is my understanding that Snap was at one point intended to be a package manager for their embedded OS, which was more locked down. Then they started pushing it to all flavors of Ubuntu.

Explain to me why, on Ubuntu systems, sudo apt install firefox installs the Snap version? Clem over at Linux Mint asked the same question, which is why Mint ships with Flatpak and not Snap support out of the box, and Mint…I’m going to get the details wrong here, either Firefox themselves packaged the APT version, or the Mint crew did, or both at various times.