Lol, getting 10 thousand users to slightly inconvenience themself even to stand against things that directly effect them is difficult. Imagine trying to get billions to do it for a slightly indirect possible effect on megacorps.
There are probably half a billion people alone that would gladly lick the boot of any mega corporation that demanded it.
It depends. Someone who is very active in the community and wants to take on the task of migrating, moderating, and keeping communities healthy are encouraged to do it.
For adoption, having 5 instances with 1000 people each is much better than 1000 instances with 5 people each.