Are you speaking purely out of principle, or do you truly believe it makes sense in this particular case?
Personally, I just can't imagine anyone paying a monthly fee just to access metadata for Steam games and nothing else. At least with Nexus Mods, you're paying for (easier) access to actual content for your games.
Probably speaking as someone who has used nexusmods in the past decade. Their monetization stuff is on the "lolwhat, that's kinda excessive" side of things.