@jjk it's not some app that decided to default to some instance, it's the official app of a project that gets identified with the whole fedi deciding to make default an instance that has 1/10th of all active accounts on fedi.
And that's a problem. I wrote why this is a problem, with some history of a similar social network a decade ago that got badly hurt in similar circumstances: https://rys.io/en/168.html