If a new user installs malware from flathub while trying out mint for the first time, they’ll probably blame mint instead of flathub. Nobody will say “damn, I should have listened to that warning” while their “discrod” app rm -rf’s their entire PC away, they’ll instead claim Linux is crap and go somewhere else. Doing this helps keep mint safe, and definitely encourages unverified FOSS apps to hurry up and get verified.