Why would anyone have uploaded their music to the archive, if 15 or 20 years later, you wanted it removed? Perhaps, you could threaten everyone that downloaded the module with a lawsuit too! It's been out there for 15 years...
I definitely will do so if I ever come up with something worth sharing.
Why would you upload it? The demoscene and the trackerscene have always been based on sharing, for free, I've never heard of anyone trying to make some money out of it. The artist still owns the copyright afaik....
Everyone starts out small at some point. An artist who makes it big was once an amateur, and many artists wouldn't want to sully their reputation by associating their name with a crappy song that they made years ago.
I suggest you take a look around various former tracker musicians websites, who have made music their professional careers. Some actually link AMP, TMA, Modland on their sites for those people who still like nostalgia and their old releases. A lot of musicians state they have a background in the demoscene, as that's where they started...
Tbh, if an artist becomes that famous, why would they care about something they did a couple of decades ago. Modules is very niche, compared to modern standards that is. I would only see an issue if someone tried passing their work off as their own or trying to make money out of their efforts.