Sometimes you specifically try to install the non-snap version, and Ubuntu just says “no, you’re getting snap”. There was a kerfuffle about Ubuntu and chrome a while back.
There is sometimes an “advantage” in being able to user a new version with your OS than you would otherwise, or not needing to try to find/download dependencies.
The downside is that it’s slower, they take up more room, they have issues when the program needs to talk to other programs, and that Canonical is creating a weird walled garden.
…also, if you want something similar-ish to snaps, with the same upside and with less downsides, use flat-packs.