I think that's because they were contractually agreed at the time, since the actors weren't on strike and had a binding contract. So they spent it paying the writers strike fund from their own pockets and turning their shows into pro union platforms.

Drew does not have this excuse at all ifaik.

No, there was a technicality actors like Conan etc were still contractually obligated to perform, and the only way they could avoid the picket lines was by not using scripts. So they couldn't write anything unless they hired scabs (which Conan said they weren't going to do). Instead of hiring scabs, Conan improvised.. Conan’s writers’ strike episodes only happened because NBC pretty much forced him back on to avoid layoffs to the non-writing staff—and that only happened because Letterman’s production company reached an interim agreement with the WGA, so Dave and Craig came back fully writered-up.

The notable exception was Ellen who famously hired scabs immediately

That’s showbiz, baby

I’m guessing there’s some contractual agreement that says they’ll take her treats if she strikes, so she protects her own self-interest instead of the greater cause.