IMO its more nuanced. They're likely in production ramp-up of the M5 Ultra Mac Studio, for release in the next ~3 months; they have pre-purchased bins of memory from the supply-constrained major memory supplies; and they need as much as they can get because they want to push an M5 Ultra config to 768gb to continue the "you can run local models" story that the M5 Max Macbook Pro started telling last week. Going beyond…
I know everyone thinks they're going to just kill it, but I don't see it. Apple's move under Tim Cook has been to exhaust supplies (see: filling the Intel Mac Pro chassis with air and not updating the CPU), letting people predict its death (see: 2013 -> 2019 Mac Pro silence), and then redesigning it into something people want while utilizing it as an opportunity to segment specs across their SKUs.
The Studio will remain the high-powered creator machine, whereas the Mac Pro will be retooled into an AI beast.