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The blue one may have a less space with a normal fork, but then you have to keep cargo and wheel separate. Hm, what would work.... oh I know, a fender and something structural. Like a fork.
I don't get the argument with the brown frame at all, they already have the necessary room built in with the frame structure taking up the space where a fork would go. Weight wise I'll bet that the custom steering linkage + the frame at the front is more than just a fork.
Imagine fitting a fork on these two bikes.... It would be quite an effort and would lead to a bigger frame, a heavier frame+fork, a compromised cargo space, the addition of a large steering linkage.
I can understand them choosing for a more complex but light and compact solution.