"But for this to work, such curators need to have a blockchain where they can profit from it."
This is only generally true.
I would pay 100% of curation rewards, and neither sell votes, nor self vote, for such a delegation, because I am not here for rewards.
There are others besides myself that would do this too.
A society is more than just an economy.
@fulltimegeek and @stellabelle have proved this.
Automate such contractual arrangements, and I will be the first in line, and I will not be alone.