I sympathize, but Bandcamp is not in the metadata business, nor do they want to be (I’ve asked them). They leave it to the artists/labels to create and upload metadata to the relevant metadata providers. Some do, some don’t, some don’t do it reliably or comprehensively. Having spoken with some independent artists about this, they just don’t have the time, inclination, or tech skills to do it. Roon is a drop in the water relative to their other revenue sources (gigs, physical albums, soft goods, widely available streaming platforms that curate their metadata), paltry as those are for most independents.
My practice now is to add/correct entries for Bandamp releases on Musicbrainz and hope those filter back to Roon, as they do eventually. If we all did that for a few releases we care about, the problem would go away 