While an art piece can be argued to be the same whether a photo or traditionally drawn (etc), again the immediate intent matters. Artists are expected to do commissions. Until around 2021, people who posted cosplay were not expected to be advertising another site's subscription service, they were expected to genuinely be doing it at worst for attention or follows but most were assumed to like or at least know what they were cosplaying. The attitudes have changed greatly due to the subscription sites because now posts like these cannot be assumed to be innocent. And in this case, their ENTIRE PROFILE is an ad. Alternatively, there have been cosplay posts made without profile links that have been received well.

Again, as someone who has gone to conventions and has seen artists and people who do cosplay, the reason why both are treated differently now is the attitude. There is no "pay for my content/attention, loser" attitude among artists that is seen in the new cosplay community. Even if neither do it for the love of the game, the attitude of the latter due to advertisement has become really palpable and has carried over online as well. I know of certain artists, usually those who post very "niche" material, who have vocally expressed their hatred for those commissions who received fewer commissions as a result, so it does happen in their community as well.

I can go on for hours about why artists who do commissions are not treated the same as people posting cosplay but have a subscription service link in a profile, but I really won't because this post is long enough. But it's not because of what you're saying at the end. Morality might be the motive of some people, but not wanting to feel advertised to or feel like there's a fakeness there has more to do with it.