It also involves around three or four "I know this could be dangerous" click-throughs. That is harder to get an audience of everyday, than settling for paying someone you are probably already paying.
It only takes 2-3 clicks once (go to settings via direct link, enable allow installs, go back and install). It is a non-issue
The average person will not click through a security warning. And if they do, they don't know what they're expected to do on that settings page. They are trained _not_ to bypass security.
They're also killing this off next year and you'll have to install via adb, unless something changed and I didn't hear about it.