People may feel more open when they are sharing a .zip rather than 'logging in' - I know a lot of people that are still opposed to 'connecting' accounts - this avoids that connection, regardless of OAuth, straight username/password, etc.,

It's not clear to a lot of people 'what exactly' they are sharing when they link accounts, but when you upload a .zip, you are ONLY sharing what's contained in that file - there really is a big difference between uploading and linking =p