Furthermore, non-solicitation of donations is a political reason to prefer uBo. I'm curious about the technical reasons. As a side note, I personally have no problem whatsoever with an extension creator soliciting donations as long as they're not doing so in a deceptive or annoying manner.
uBlock hasn't been updated in almost a year. uBlock Origin is actively developed. uBlock has effectively had no significant changes or improvements since the uBlock Origin fork happened.
There's some background here which might be relevant. Another extension, AdBlock, used to have a policy against "acceptable ads." The author sought donations to keep development going, but later sold the business (and the users!) to an entity that immediately started allowing such ads through.
Maybe the author of uBlock Origin wants to make it clear that this can't happen here.
I can say anecdotally, that I found plain uBlock more featureful for everyday usage, but I haven't done a thorough review. I currently use uBlock Origin.
[0]https://github.com/chrisaljoudi/ublock [1]https://www.purify-app.com/