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.

@omgubuntu Right. Instead of saying, "Thing is great, you have no choice to adopt it for XYZ. Oh, it broke something? Too bad!" the Flatpak approach was, "we'll make this thing available, and let people offer their apps on it. Oh, people like it? Great!"

They let people make their own decisions, and had it prove its benefit.