Why is it just the compiler maker’s job to report it may (read: will) underperform on AMD and not also the program developer too? If I paid for software that performed worse on AMD because it deliberately hobbled itself (and was not informed), I’d want a refund.

It’s straight up anti-competitive, but consumers aren’t smart enough to understand that it’s a problem; A consumer just sees biased benchmarks that show Intel outperforming AMD, and then choose Intel.