Earlier quoted context omitted.
Don't know why you are downvoted since you are completely correct. It is unfair to the developer but we wouldn't even have this discussion if people rejected app stores. I like that more developers just reject software certification processes. There is zero benefit aside from lock in.
Other than open season on the users with malware out the wazoo. But who cares about security. Do you buy healthcare from the back of a pickup truck?
You could still have trust mechanisms while downloading from sites where the author, not the walled garden, has the control.