The problem for anyone wanting to build an older generation fab is cost. It costs (within an order of magnitude) the same to build a modern fab as it does to b

The problem for anyone wanting to build an older generation fab is cost. It costs (within an order of magnitude) the same to build a modern fab as it does to build one for a process 1-5 generations back, maybe more. You have a roughly similar backlog for equipment too. For your troubles you get far fewer chips per wafer so your cost per chip is higher. And the chips are slower and use more power. That makes it much harder to get any kind of payback on a depreciating asset that only gets more out of date. You also risk demand for your new 45-nm or 90-nm fab dropping off toward zero in 10 years. Historically older fabs would see a drop-off in business as new chips were designed for new processes so as time went on there was more and more capacity available for cheap on the older nodes. That cycle is and has been slowing down though so there isn't much slack even for older fabs. I'm not sure where the market will end up. If the current shortages are a temporary backlog + hoarding then things will work themselves out within 1-3 years and anyone starting lots of fab construction risks bankruptcy - something that has happened multiple times in the past as keeping a fab idle is equivalent to burning it down so you end up having to dump chips at cost or even a small loss. On the flip side if the recent disruptions are merely accelerating an existing trend then anyone kicking off fab construction stands to make a lot of money.