i suspect that TSMC doesn't have as big a monopoly as you've made it out to be, not because intel is competing, but because the customers of TSMC are large enough that they "force" the innovation (aka, they "threaten" to not use them if they stop innovating).
Also, TSMC hasn't been around long enough to become the slow behemoths that other big monopolies have become.
TSMC doesn’t have a real monopoly, they’re just a few years ahead of everyone else in integrating ASML’s latest tech. Samsung and Intel aren’t very far behind. The more money TSMC charges the more incentive the others have to catch up but they can only move so fast. GlobalFoundries and STMicroelectronics seem stuck in the double digits.
It makes a big difference to a few competitive customers so TSMC gets paid well for that first mover advantage, but yeah it’s not well secured monopoly.
thinking that TSMC is "just" integrating ASML tech is a common but big misconception
ASML tech is a tool, one essential for new better chips but not sufficient
You also need to have a lot of know how about how to best use the tool, integrate it in workflows etc. where TSMC seems to be somehow ahead of Intel.
Additionally the custom tooling in the steps leading up to the use of ASML tooling are also hugely important and TSMC is quite a bit ahead of intel with that. It turned out having multiple different customers with different needs which all collaborate with TSMC to optimize the tools in their workflows.
I think it's just a matter of 'if you stop innovating, others will catch up quicker than you expect'. It's a continual r&d March, and you don't want to end up like Intel and get stuck on 14nm forever
And Intel was a company that was still shoving billions into r&d, yet still got stuck
So much of the tech industry has Moore's law baked into the supply chain forecasts, so lots of incentive to deliver on it.
Also, TSMC hasn't been around long enough to become the slow behemoths that other big monopolies have become.