I think part of the problem is that cargo bikes in general are using unique approaches to the point that they pretty much all have a few completely specific components even with the smaller brands.
My bakfiets doesn't really have anything that's specific. Ok, the kick stand, but that's part of the frame. The ball joints in the steering arm are also standard I think.
bakfiets is maybe not the best example but even still the forks. Some use 2 steering arms, some one, some still 1" steerer tubes, often times still roller brakes so path to upgrade is not great etc etc etc.
I think part of the problem is that cargo bikes in general are using unique approaches to the point that they pretty much all have a few completely specific components even with the smaller brands.