You can install your own APK already. It's only slightly inconvenient. But apparently that's inconvenient enough to get zero business.
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.
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.