Lack of interest from standards committee and browser vendors seems to be the only thing stalling:
https://github.com/w3c/IndexedDB/issues/230
I personally think that this stall is simply a symptom of the larger issue that the IndexedDB standard was bad to begin with, and that lead to lax adoption from developers, which deprioritized vendors from fixing the standard, leading to a vicious cycle where even a seemingly trivial issue like adding BigInt support goes unimplemented.
I personally think that IndexedDB is salvageable, and not only that, it has the potential to be an amazing web API. But the way things are progressing with the standards committee, I very much doubt it will be any better in the foreseeable future.
Yeah, they definitely stopped investing in the APIs themselves. If someone can make a polyfill to shoe-horn in the functionality, then they don't really see a need. Which is sad, as we have outsourced our future to TypeScript, React, etc.