Why? I've heard this for years at this point, but as someone who rarely uses snaps because they're the only convenient option for software I'm using, I'm generally ambivalent about them.
People seem to hold really strong opinions about snap but I've never been able to get a straight answer, just a bunch of hand waving.
So that's admittedly not a good look for canonical, but my read of that is that if you're getting widely-known software from a developer who's publishing it to snap themselves, and you're cautious about your usage, snap is fine.
For example, essentially my only use of snap is to install certbot. If I follow the directions from certbot.eff.org precisely, then I'll get certbot installed and no issues.
I certainly agree that (a) the system is ripe for abuse and (b) should be self-hostable to support Free software. Both of these could be fixed by canonical opening it up.
My biggest hit was when they pushed browsers to snaps, and I couldn't do some of my school projects because my school stuff was on a separate disk that the snap was not allowed to access. (Had to use o365, and wasn't installing windows to write my papers)