Some subs went to allow NSFW (and porn) as protest, as you said, and reddit admins disabled the NSFW tag on those subs which decided to allow porn and become NSFW.
To add to that, if a sub is tagged as nsfw, there are no ads (to not scare of advertisers).
Some sub mods indirectly invited users to post porn, so they became nsfw subs by protest.
It sounds like they're just removing the NSFW tag site-wide instead of using the manpower to manually check each sub to see if it was NSFW before the protests.
What a fucking fumble, using the iron fist approach on the people who supply and moderate literally all of their content for free surely won't have any repercussions.