But UAC wouldn't have prevented that as there is no guarantee that people won't just allow the action or dismiss the UAC intervention.
You can always say yes and bypass the security... Like disabling your antivirus, setting an exclusion, think that something is a false positive.
UAC just block elevation. And do it very very well. If you're installing a clean software, ok, go ahead. But, if you're doing nothing and some strange program asks for elevated rights, well, you have at least a warning.
You can always bypass the security...