People have been upset about the direction of Twitter, for a variety of reasons, since Elon bought it. BlueSky was simply the best alternative available when people began leaving Twitter in droves. I don't think you can assign intent to the creation of the platform, which predates all of this.

I also think it's naive to accuse any particular group of people to be more or less prone to seeking echo chambers. That's endemic to humans in general, though certainly not completely pervasive.