Given Google's track record, I don't think it's just "being upset" to have serious doubts about the probability of this escape hatch staying indefinitely.
Given that google is now forced to have competing app stores due to Epic v. Google and the ninth circuit courts went into long and arduous detail in that anti-trust case about sideloading restrictions I don't think they have a leg to stand on if they get rid of sideloading completely. Oddly Apple continues to get away with it no problem.
They've been chipping away at AOSP for years, pulling more and more parts of the Android experience into their proprietary Google Play Services. In this case, they're doubling down in the same direction. Sure, it may be more or less transparent from a user-facing perspective, but it's a fundamental change to the model.
Previously, it was ultimately a local decision: Android warned you, you enabled the permission, and you installed the APK. It now becomes dependent on a Google-controlled verification/authorization mechanism. That's fundamentally different from making the existing "unknown sources" toggle more annoying.