They already do, but partially. You can upload anything, but can't make it public if they match the title to something known. I don't know what's the threshold / database they use, but if you want to see the message, try to call something "City of stars, la la land" and upload.
The new "official scores" are an exception; you can't even see them without paying. A step backwards in my opinion.
If you really want one of my musescore files, send me a message and I'll be happy to email it. Odds are other people on the site will do similarly.