They might front the money, but don't own them. Apple gladly lets someone else own and operate the fabs and take the risk (which is smaller with Apple as a client)

Let's not forget that a 7nm fab has a very limited period of usefulness for the likes of Apple etc. That leading edge is always moving forward and while it might be financially viable for some aspects of the process to be upgraded to the next node, that's not always the case and that's where TSMC's hundreds of other customers join in and the (now old) equipment can be still used for many more years.

Edit: But perhaps with the exclusivity deals, the likes of TSMC are less reliant on spreading the cost over 15+ years than they used to be. To be clear, I was talking about long-term use.

The leading edge has slowed down a lot. Apple is still selling M1 chips and AMD is just now releasing new models of zen3 AM4 chips.

There is more co development and risk sharing than you think. TSMC has nodes only apple uses.

They do, but as far as I know those nodes are just early/late verisons and tweaks to the main, popular process.

But if Apple pays TSMC $$$$$$$$ in advance to build a 2nm node production line especially for Apple, and it turns out the 2nm node doesn't deliver the hoped-for improvements in power efficiency? The money's already spent.