What problem does this solve or what need does it fill?

This field is (nearly) unused, and inaccessible. It adds more conceptual overload for no advantage.

What solution would you like?

Delete the field!

Additional context

This may be planned feature work, but I don't think so. Subassets having metadata doesn't make much sense as far as I can tell, and the root asset has its metadata passed in and it isn't changed. The only part that's a little confusing is the populate_hashes argument, but that only affects the loader dependencies, not the asset's meta field.