Why should it be short term, though?

If it takes 4 years to build a new fab and Apple is willing to commit to paying pay the price of an entire fab, for chips to be delivered in 4 years time - why not take the order and build the capacity?

I mean, these things are likely already written down and Apple still gets lots of capacity for the reasons you mention.

But Nvidia has also spent billions/year in TSMC for more than a decade and this just keeps increasing.