To me it also seems to be a case of jumping the bandwagon, it's just popular apparantly to easily dismiss the Kubel/Schwimmwagen/Tank Car (I wonder how many actually gave them a chance and adapted their driving style/expectations accordingly).
Another thing is that they need a different context or mindset to be appreciated or even understood for what they are, that's not something everyone is willing to do it seems.
I'll agree that driving a stock Kubel/Schwimmwagen on tarmac is a rather dull experience (at least in a videogame) but when you tune them and spend some time working on a proper set up suited for these cars (not focussing on raw speed which is a pointless pursuit) they become huge fun, especially offroad and offer something nothing else does.
But yeah, I'm probably preaching to the converted anyway, the point of these cars is that there is none really, you either love or grow to love them like any other car or you don't but I guess it's also very helpful to have a sense of humour as that's probably the main issue for the hate displayed for these cars.
If you only want serious driving/racing machinery and can't have a laugh at the ridiculous notion of racing Third Reich war machinery or a huge tank-engined custom car on a schoolbus chassis, then perhaps you're taking things, well, a bit too serious frankly.