Why was something like this not released on day one?

Is the bad privacy ptactices in some apps actually due to the React project not caring about android and/or privacy?

Not releasing it immediately doesn't mean they don't care for Android or privacy. You're being very disingenuous.

Development teams have backlogs and scoped storage is still very recent. It's normal for Flutter, React Native and the like to take time to catch up.

And you didn't even see many people immediately switch on native development. The APIs were a quite a bit more complex than what people were used to, so a good abstraction need to be reasoned about as well.

Due to Google enforcing scoped storage, development started going faster on all fronts.

This didn't drop out of the blue. And users had been asking for this for ages. Google had been talking about these changes (there were some others starting android 8)

A hobbyist project I work on changed release schedules and new functions to be able to support this on day one. A major framework backed by $$$ should be able to do the same and not lag 2 yrs behind.