DME only on LOC Approaches

[tebak41732]

Can anybody provide any insight as to why at least in Australia you can only use a DME for a LOC approach? I've heard that apparently you cannot use GNSS to reference the position of the ILS but can't find any reference or material to support this one way or another.

Edit: Should have been clearer, some approaches give you the option of referencing a VOR using the GNSS, but no approaches that I've found allow you to use the GNSS to reference the ILS itself e.g. putting IAV into your flight plan