That's one way it happens, but in general the term appears to be about decline in quality for the purposes of profit-seeking, regardless of whether services were offered for free or not.

The wiki article starts with this:

Enshittification, also known as crapification and platform decay, is the term used to describe the pattern in which online products and services decline in quality over time. Initially, vendors create high-quality offerings to attract users, then they degrade those offerings to better serve business customers, and finally degrade their services to users and business customers to maximize profits for shareholders.

Other articles I looked at seem to agree with this basic concept.

And like I said, spam from scammers and inbox spam are examples of shittiness that seep in regardless of if you engage or not. There is no "no marketplace plz" option, and even if there were scammers can still send you friend request spam.

[–] [email protected] 1 points 57 minutes ago

Eh, maybe I'm being pedantic, but I still don't really see how the addition of the steam marketplace is an example of the steam platform declining in quality. It was a feature that they added a long time ago, and it doesn't interfere with or worsen the experience of buying, organizing, or playing my video games. Sure it's a needless addition (in our opinions), but one that I can easily ignore because it's so isolated from the main product. Plenty of other products and services out there have features that some don't like or don't use, but that isn't the same thing as enshittification. And I feel like the spam would happen regardless of if the marketplace was there or not. That feels more like a moderation problem, not an enshittification problem.