It's the fact that, as the Base author, you don't really know how a given application might present a 16-byte binary version of a UUID to the database. If you don't know that, how can you reverse it to display the correct string representation? There are complications with byte groups potentially being in different places, and even the potential of mixed byte ordering.

How can Base make a 16-byte binary format that display both a GUID stored from a .Net application from person A, and also a UUID from a Python application from person B, and have the string representation be accurate in both cases? I don't think you can.