Think about it from a less technical perspective: I can install an app from the official Google Play store that voids my warranty.
They can't have that on their public facing store. Google wants users to install apps, they don't want them to be afraid of voiding their warranty.
It's interesting to see how things played out over the last few years.
Google has been moving towards a more controlled environment, from something that was initially billed as open.
Apple started completely locked down with a strong customer focus, and has cautiously been making their policies more developer friendly.
I personally prefer Apple's approach, as it was always about the end user — but as a developer I was sometimes envious of Google's lenient policy. Google's assertion of control now makes me more interested in developing for their platform.