They never did. Releasing the source contributed creating the developers ecosystem we have today. What Google fears more than the Armageddon would be someone making a truly FOSS operating system capable of running on Android devices, and they prevent that by keeping device drivers and firmware tightly locked.

IMO Android is working towards having a compatibility layer so that drivers can be freely shared across distros.

Look up Project Treble.

That still requires cooperation from the SoC vendors. If they aren't interested then Treble will go nowhere.

Treble is required by the Vendor Test Suite for Android 8 and higher. https://source.android.com/devices/architecture

This is probably still in Google's best interest, since it greatly reduces the cost for OEMs to distribute updates (and updates are one area where Android severely lags behind iOS)