the normal way to do that is by hiring/firing to meet demand, but in the fab business, you have 10s of billions of dollars of capex with relatively little opex. if you're running at <90% capacity, you're losing money.

Factories working at (significantly) less than full capacity gets a bit harder when you've got one of the most expensive machines on earth working in them, and production lines that'll be out of date in a couple of years