There’s a semantic difference between “supporting mods” and “provide support for modded installations”. The former is fairly common and is what steam workshop is about and is what you are talking about.
The latter is basically unheard of (for what I hope are obvious reasons).
The OP is a bit ambiguous about which of the two or is.
Deleting accounts doesn’t mean the company deletes your data. Even under GDPR (Everyone else is completely SOL here, I believe), they can keep if it is required for their business, unless you explicitly demand a full deletion.