You could also ask why AMD and Intel are not more proactive at locking down DDR5 chips and making sure they are available at reasonable prices.
They produce millions of dies that all depend on other companies DDR5 chips to even produce a beep. Without DRAM they are just sand vendors.
One might think they could by default bundle them like a box, order years of production upfront, like they do for GPUs.
But no.
These companies don't plan well enough into the future. That's the reason.

There's only so many ASML machines and wafers to go round even if they did make it.