Well, I really don't want to put the blame on anyone. Misbehaving apps on casual users' phones are a legitimate problem, and the OS is expected to mitigate that. Moreover, there are not many proven models for that, and they all entail compromising someone's convenience (either users', devs', or both). You can't have your cake and eat it, too.

In this specific case, though - especially given that the project had no iPhone version due to technological constraints - Android as a platform moving in that direction is probably the biggest reason why it became too hard to develop the project further. And the direction of Android development is set by BigTech, so you probably could justify calling them "the big obstacle".

It's important to note that the movement towards security-by-default is larger than just some subset of BigTech. It's how the whole industry tries to cope with computing becoming ubiquitous and trusted at the same time. It's Eternal September, but now the new users have banking apps on their phones. It's a hard problem, and every attempt to date has always resulted in users and developers losing some freedom. This OP just highlights the consequences of this movement for a particular project.