Since the primary motivation for people switching to App.net was them getting upset at Twitter, they slowed down the frequency and breadth of the changes they were making to their service so as to upset fewer people and less frequently. In the end, this was a positive outcome for users that liked Twitter exactly the way it used to be and didn't want it to change.
Of course, Twitter's changes may not have been motivated by App.net at all, but even if not there was still an escape hatch for users if things got too bad.
Except they couldn't. They had to be invited or pay for it. In those days circa 2012, it was a hype train among a niche crowd.