As far as I can tell, none of the companies producing memory chips are increasing production because they don't know if the current demand is sustainable.

Increasing memory production capacity is a multi-year project, but in a few years, the LLM companies creating the current demand might all have run out of money. If demand craters just as supply increases, prices will drastically decrease, which none of these companies want.

You are wrong. Memory production is being expanded in 2026 and will expand further in 2027 and 2028 as the memory suppliers catch up on fab shell capacity.