OpticalMoose
You haven't heard about wearable servers? C'mon get with the times! I'm headed out for a jog now, gotta keep my hashrate up!
vlemmy disappeared (alternate link) a few weeks ago with out a trace or any explaination. FMHY's domain was confiscated by the government of Mali.
That's especially a problem since people absolutely don't want to see ads, they don't like the idea of a coin/reward system, and generally don't contribute (less than 1 out of 20 ppl donate, and that's being generous)
In addition to what the others have said, we've lost some big and popular instances (Vlemmy, FMHY and others) along with the communities they had. Also, with the 2 biggest (lemmy.world and lemmy.ml) coming under attack every week, some users want to be on a smaller instance that's under the radar.
Finally, people want to choose an instance that fits their interests/beliefs. I chose mine mainly for what they don't allow and who they're defederated from, but to each his own.