Why tsmc would agree to this is simply economics. More demand and a rich customer causes prices to rise for other customers of tsmc. That is if new customers is willing to pay higher prices, that causes other customers to also have to pay higher prices or risk losing out their spot. Tsmc is the best manufacturer right now and if they want to keep that position, they will have to continue their spending war. Higher profits helps this out.
Intel on the other hand has no chance of amortizing 100 billion dollars on fabs and recouping the spending over 3 years. They are more and more likely to go fabless and commit r and d to architecture and software because that is the only way they can get back to tick tock(something the new ceo has committed too). R and d for process and keeping their fabs up to date is too expensive. Unless revenue grows exponentially soon, they won't be able to do it
On top of this, AMD gets crippled if intel outsources manufacturing to TSMC. I think TSMC will have no problem taking intels money over AMD because they can pay better than anyone and help raise wafer prices. Because intel does not make consoles and intel is already charging 300 to 500 dollar for what are small chips, they can pay high pricing that can even intimidate even Apple. AMD is making TSMC 9 percent of its revenue while Apple is making 25 percent of TSMC revenue. Do you not think Intel could be a similar size to Apple when Nvidia is barely making anything with tsmc this year and is still a 5 to 6 percent revenue share customer? On top of this, intel can pay way higher prices considering the savings on not buying new fabs, would be 10s of billions of dollars.