Do you know where this is confirmed? I have also read today that onsite international guests will be able to book 7 days in advance but offsite guests have to wait until they are in the US.
It annoys me that the use this excuse without saying why! About a year ago they changed the system for booking dining, and at exactly the same time UK residents (I'm not sure about the rest of the EU) lost functionality from the app and had to start using a VPN for most ADRs and dining changes on the website. There were no changes in UK law at the time, so they most have done something to make the app less compliant. It would have to be something very dodgy to make it illegal in so many countries.

As we were able to use the full functionality for so many years I'm sure they could do it again with a bit of effort.
If you contact them to ask about this the advice is to ask your
travel agent to book your ADRs for you! It doesn't really make much sense that a UK based travel agent can book if the system isn't legal in this country. If they give the same answer this time can I ask member services to book my LLs for me?