Their decision not to fix is not the problem, their decision to keep the flaw a secret and sell products with a performance expectation set and then release patches that slow down that paid for performance is.
Anyone who needs out-of-the-box performance can get it if they're willing to accept out-of-the-box security. Of course that doesn't make these side-channel attacks any less frustrating. For instance the original Meltdown and Spectre attacks were on my mind when I chose to "vote with my dollar" and buy an AMD CPU, only to end up with Zenbleed this year lol
They shouldn't have to accept OOB security flaw that was not disclosed intentionally at the time of purchase. If intel just made that information public when they found out, your argument would be valid. They could have also purchased different processors.