Scan QR code -- you don't have our "captcha app" installed, automatically redirect to Play store -- download malware because Google Play's horrible screening -- profit

I must not be the first one to think of this, right?

Right???

Hey at least in September they're going to stop you from installing F-Droid. For your safety, citizen!

Yeah, idiots would fall for it.

Both (Google/Apple) need a much higher level of certification for anything to be allowed to be prompted to install. Either you're already big (and can easily afford to pay for some human time to verify), or you're a manufacturer selling something that has an associated app (again, which implies you're reasonably big and can afford to pay for verification.)

You're neither? Get lost. Somebody types in the name of the app, fine, but the user must find it.