I dare say that allowing any distro to use their repos is pretty generous, and gives back to the community. They have no obligation to open source Snapcraft's server, and snapd being able to install snaps locally is more than enough.
https://forum.snapcraft.io/t/download-snaps-and-install-offline/15713
Pretty much. Canonical made a few questionable choices in the past but overall they've done a lot for the Linux community. And their distro is very good. There is a reason why distros choose it as their base.