Then there were software libraries and the Intel C/C++ Compiler that favored Intel. They would place optimized code paths that only ran on Intel hardware in third party software. Intel has stopped doing that in recent years as far as I know (the MKL has Zen specific code paths), but that is a fairly recent change (maybe the past 5 years).

There were also ISA extensions. Even if Intel had trouble competing on existing code, they would often extend the ISA to gain a temporary advantage over their competitors by enabling developers to write more optimal code paths that would run only on Intel’s most recent CPUs. They have done less of that ever since the AVX-512 disaster, but Intel still is the one defining ISA extensions and it historically gained a short term advantage whenever it did.

Interestingly, the situation is somewhat inverted as of late given Intel’s failure to implement the AVX-512 family of extensions in consumer CPUs in a sane way, when AMD succeeded. Intel now is at a disadvantage to AMD because od its own ISA extension. They recently made AVX-10 to try to fix that, but it adds nothing that was not already in AVX-512, so AMD CPUs after Zen 3 would have equivalent code paths from AVX-512, even without implementing AVX-10.