A couple of things come to mind here:
I own a metal one which I assume was dishwasher safe but somehow water got trapped inside the ‘extra’ parts of it which could be unsanitary due to the water eventually stagnating.
Another is that the heat from the dishwasher can warp and silicone or plastic parts which will render them unusable eventually.
Not saying you’re wrong but this is what I consider from the warning they provide.
A bummer that they host these on archive and it’s down at the moment :(