Throwaway rooms were used for different purposes. One was to open up the 60 day window for off-site stays - a loophole Disney cares very much about and was closed. This is/was an easy fix.
Another was to get better fastpasses toward the end of a split stay - for some people it was worth paying the $100-ish/night so that (for example) their last FP day in the parks was 60+6 instead of 60+3. Which (IMHO) Disney doesn't care about. But they DO care about people doing the same thing but cancelling the room a week out.
And apparently changing the
MDE code to delete FPs that were only obtained 'fraudulently' but keeping those where people legitimately made last minute changes to their reservations is very difficult. So at least for the moment MDE isn't allowing the FP window to be open across a split stay (except when it does for some people for no discernible reason). Meanwhile, over on the DVC side there are CMs who say that once the FP changes 'shake out' DVC split stays will be considered continuous and not just consecutive. Your mileage will almost certainly vary.