Patents is not the issue here. Not even close.

The up-front investment of a memory fab is measured in billions, and takes years to construct and get running. The margin on the chips themselves is terrible, so without scale its not worth even trying. DDR5 is a industry standard that takes some effort to conform to, but the licence fees is a drop in the bucket to the cost of creating a fab.

The fabricators were cautious about increasing production, and slow to start planning. It takes further time to build up capacity, and if the demand drops down, they may end up producing dram at a loss when the market flips over to oversupply. The demand whiplash could kill any company that dared betting on increasing production. See the "bullwhip effect" https://en.wikipedia.org/wiki/Bullwhip_effect which has killed semiconductor fabricators before.

There is a discussion to be had about how to maintain national semiconductor production in Europe and US as a strategic industry, but historic attempts have all failed.

Billions is nothing in this market - if the market is supply constrained in the medium term then the hyperscalers will purchase their own route to manufacture (e.g. through coinvestment).

Also that's not what the bullwhip effect is - although I know what you are saying. The bullwhip scenario is about the effect of communication and batching through various layers in the supply chain, this is more similar to the cobweb effect/theory.