It's not that simple from the manufacturers perspective.

Setting up a new fab takes years. Usually 5 or more for a grounds up build. Less for an upgrade (1-2 years or so). Lots of in-progress fabs have been sped up and we will see more supply sooner, but not soon enough.

Making less HBM and more DDR RAM doesn't make sense for $hareholders, so we are stuck with getting supply at a trickle such that the marginal cost for both is equal or it's a contract with a penalty larger than any profits