The key is that while there were many clones of x86, there never really was an attempt at a company built around "run MS Windows programs natively" because maintaining software compatability is an order of magnitude harder than doing it for hardware.
Moreover, companies aren't buying GPUs to keep their huge stable of legacy applications running. They want to create new AI applications and CUDA is a simple API for doing that (at a certain level).
Microsoft's entire history is around building a moat of APIs because the PC software industries has a wide variety. Nvidia has, so far, been focused on building actually useful things for developers. Basically, where all the other manufacturers viewed their chips as special purpose devices, Nvidia allowed developers to treat their chips as generic parallel processors and this facilitated the current AI revolution/bubble. Now that Nvidia has created this market, it can charge by the use rather than charging by processing power. The thing is that Nvidia's large potential competitors simply don't want to create clones even if they could - because clones would have to be sold by processing power rather than with a markup for their usefulness. It's worth looking at the list of x86 compatible makers [1]. Making an x86 wasn't quite something you could do in your garage but clearly the barriers to entry weren't huge. But any Nvidia compatible is going to cost a large amount of capital but can only sell by processor power and so AMD, Intel and similar sized entities don't have an interest in doing this.
Nvidia and standard-maker is limited in what breaking changes they introduce - these can harm their customers as much as they harm the competition. Intel failed to force all their changes on AMD as the xxx86 market expanded (notably, the current iteration of CPUs standards was set by AMD after Intel was unable to sell their completely new standard).
Still, I'd acknowledge that "business sense" today follows the approach of only aiming for markets the company can completely control and by that measure, CUDA compatibility isn't desirable.