For a CPU vendor, ISA is very relevant: most buyers will start their buying decision with ISA choice already fixed, and a vendor who can't offer a CPU with that ISA simply isn't in the race.
It does not matter whether you are a believer in horses for courses when it comes to ISA, or a believer in "frontend ISA does not matter because it's all translated away anyways": when buyers don't want what you have, you are out. And buyers are more like a stampeding herd than like rational actors when it comes to ISA choice. I'd see offering CPU for multiple ISA as an important hedge against the herd changing direction.