well, in their place of birth, not many. because unregistered friesians aren't worth shit here, and many people distrust them.
the majority of the population is IN the netherlands. you can't blame KFPS and its breeders for what unregistered breeders do. KFPS requires testing, and fines risk pairings. so KFPS *and* her registered breeders DO care about dwarfism.
i am not disagreeing that it's time to add in new blood (carefully, like certain dog breeds have shown before, well thought-out outcrossing), and the KFPS are looking into that as well. there are various ongoing studies right now with various research universities (WUR being one) where they are testing the majority of the population and running simulations and more. they are still, every day, trying to identify more issues, where they originated from, and what is the best way forward.
do i agree with them not opening studbooks now? no, but they are unfortunately not the only studbook suffering bad inbreeding (QH, TB, Welsh, Clydes, for some examples) that are not yet opening. so i'm unsure why the conversation is always only reduced to friesians. it's a global horse-breed issue, really. some worse than others. but every "pure" breed, faces this to a degree, and some are not worse than friesians... afaik there are studies that show iirc clyde's are even higher (if i'm not mistaken, it's been years).
however, i am responding to your claim about dwarfism and that is simply not entirely true. unregistered friesians aren't worth that much in this part of the world, and many people are passionate about their preservation also for cultural/heritage reasons (whether you agree with it, or not) and so it seems to me that the not-testing is something that you are facing elsewhere. i'm not saying it doesn't happen here AT ALL, before that claim is made, but that the numbers are exponentially lower.
and yes - i am a breeder and fan of the breed who is in favour of outcrossing, anyway. i don't personally believe the studbook is doing all it can but it's certainly doing more than most with the amount of effort they are putting into science as well. i wish other breed associations would look at this as an example and a warning, and follow suit, instead of still encouraging modern day close inbreeding (which is not popular in this particular studbook at all anymore).