So that brand-new fab has to pay for itself within the first 3-5 years, or it'll simply never pay for itself. But indeed, once it has paid off its initial construction costs it'll happily keep running for another 10+ years, churning out pure profit.

An additional problem here is that the costs have been rapidly increasing as the nodes have gotten more advanced. The tech for something like, say, the 40nm node is now mature enough that building new fabs isn't too expensive, so there's a decent market for building new ancient fabs for cheap mass production. But with EUV everything has gotten so complicated that there's no reasonable way to make it cheaper as it matures, and scale-wise you're well into the diminishing returns for everything which isn't logic. It is very much doubtful whether building brand-new 7nm-and-smaller fabs for mass production will ever make economic sense.