Do you see the direction they're heading? They're now making it so maybe .5% of android users know how to sideload. They're clearly chipping away at it, even though they might not be making all the changes at once.
What fraction of users do you think have a legitimate need to sideload apps on Android? I would imagine it's much less than 0.5%. Developers and technically-minded power users must be a tiny minority amongst Android users given that it has an install base in the billions.
Right now, not many. My point is that they aren't flipping a giant switch from an open platform to a closed platform. They're boiling the frog -- slowly removing features until all choice is gone.
A few more years in this direction and Android can be as locked down as iPhone before Apple was forced to allow sideloading