Technical stuff aside, a major reason why Flatpak does not get the hate Snap does is because users don't resent it.

There are 2 things people hate: the way things are, and change.

Ubuntu put Snaps on users desktops without asking if they wanted them. They just did it, then closed off ways to opt-out/avoid them (Cf. Firefox).

Forced change fosters resentment.

No distro made Flatpaks default/required/opt-out. Users had time to come to the tech and adopt it on their own terms/needs.

Just IMO.

It's a glib comparison but Snaps remind me a bit of that time Apple put a (free) U2 album on everyone's iPod/iPhone and assumed everyone would be grateful but people were REALLY annoyed by it.
@omgubuntu technically, SteamOS is sort-of Flatpak defaulted since the main OS is locked :P
@gamingonlinux
In the realm of gaming it helps to have flatpak since it's always the most updated version and correct libraries. Emulators and games just need to run good in their sandbox on whatever setup the desktop and kernel setup. I've been using chimeraos on a handheld PC and it's not always perfect but it's a smooth experience
@omgubuntu