Possibly conspiratorial thinking on my part, but the first reason I can think of is that those subs are both popular enough that they wouldn't want them fully migrating off reddit/closed forever, but also the kind of sub to not go along with unpopular decisions/ cause trouble. If you were looking to force a few subs open to serve as an example to mods of other subs that they must reopen or be replaced, you'd want to choose ones that aren't as likely to reopen on their own anyway after awhile, and who's moderation team you might want to replace, as you now have an excuse and the people who would get mad already are.

I wonder if it’s because they know the first few subs to be forced open will make headlines, but the second batch most likely won’t. So by starting with fringe subs it paints the picture that’s it’s not the bigger or more important subs that are participating in the blackout.

I wouldn’t be surprised to see the /r/antiwork mod’s disastrous appearance on Fox News become a talking point again paired with this, so that when people hear “Reddit forces mods to…” that’s the sort of person the public pictures.