From what I have observed in platform teams that I worked with, this is actually pretty rare. Only later down the road, when “platform as a product” is actually really established, or there have been outages (stop-the-world moment for all devs) that demonstrate how such a platform is “critical infrastructure”, QA becomes a thing and people coming from that background are considered for the platform team.
My best guess on the reason for that is that IDPs are for developers and most developers cultivate a dislike for QA - making platform owners of not well-established platforms think that having QA personas might be a communication nightmare.
I am personally thinking the opposite - someone that brings the QA perspective to the platform team is invaluable.