OpenAI abruptly bought 40% of global supply, and announced it.

Other companies found out about it when OpenAI announced and thought holy shit, if we hadn't heard of this massive deal, what else haven't we heard of?!, and so they started panic buying.

On top of that, because of US tariffs and trade restrictions, the Chinese "B-tier" memory companies, who usually buy old machines from the big 3 (SK-Hynix, Samsung, Micron) and sell this lower spec RAM at lower margins, didn't buy up these machines as much as they usually do. They weren't sure they'd be able to make a profit given their lower margins, should tariffs suddenly change again or other restrictions get put in place.