They do explain that in the post: because of the missing reciprocity. They didn't do it so OpenAI could profit off other's work, but to build a community with others. It's a pretty common motivator for humans.
edit: I think what bothers me is it seems like a Luddite reaction of someone who resents progress they don't approve of and want no part of it
The same way protesting anything helps anyone. It draws attention to a problem and, if the protest is visible enough, leads to positive change.
In the 1960s If the US wasn’t in a cold war and didn’t care that they were perceived as racists , The Civil Rights Movement would probably have to moved towards the Malcom X direction than Kings.
Sounds like it's just that the deal has changed, so they don't like the new deal and have decided to opt out.
If something is produced where the author is upset afterwards when this good is not used in the way he/she intended to, than it's the problem of the author in the first place to have choosen the wrong license.