Framing this as some intentional and strategic decision by Disney and not some legal or IT related thing seems incorrect. I’ll be very surprised if there isn’t an official Disney solution to this with time.
I suppose that you would hope that a company that cared about all of it's customers would have the solution in place in advance of making the announcements yesterday.
In all likelihood, they haven't realised in the last 25 hours that their current system will not allow international guests to book. That means, that they knew in advance of yesterday's announcement.
Disney didn't make a pre-announcement, which, after which, they realised that international guests couldn't book in advance, but still needed to make the announcement yesterday, so will fix it later (and not within the next 28 days, otherwise they wouldn't need to tell international guests that they couldn't book in advance).
Therefore, Disney decided to make the announcement yesterday, knowing that international guests would be unable to book, and then held onto that information to try to slide it out afterwards while everyone was talking about the other aspects of it.
GDPR came into force in 2018, but Fastpass+ was available until 2021.
We can make payments for dining in advance, so it's not a monetary issue.
The interesting question will be whether Americans will be able to make the bookings on their website, or whether it is app only.
If that is the case, then that would be different to Fastpass+, which could be done on the website.
However, I can start a booking on the app before moving to the website and can reach the checkout page on the app for a Cinderella's Royal Table booking for August, so unless I couldn't finish the transaction, then what is the difference? One reservation is for a time to enter a building that serves food, and one reservation is for a time to enter a building that serves a ride.
So, unless they are not going to add the infrastructure to the website, I can't see the difference.