Maybe one of the reasons social platform become annoying or not at useful over time is that, when we start using them, we join with an initial group of people. And it's easy to create a persona around that specific crowd. We can hone our persona and become the person we want to be online. We control our own identity.
But as a wider variety of people from different aspects of our lives join, it becomes increasingly harder to maintain that single persona. You broaden your persona until you've become the most vanilla version of yourself. The opposite is also true. Those who cling to their single persona despite the variety of friends that follow them can alienate their friends/family who don't know them in that context. Friends and family find it disorienting and uncomfortable to see a foreign persona played out online that may not match their real life interactions.
The emergence of a new social network is the promise to start over. To become someone new without the baggage and the audience of the past. Each jump to a new network is a redefinition of our self-image in a new context.
Humans continually change and slough off the past. But social networks don't let us escape the past. They help the past catch up with us. So we jump ship. Swim.