Is it really just because "A" is so inflexible with the floor plan of the extension that they can't place the entrance at the front?
Their flexibility is exhausted by attaching the extension to a different main house than the one specified in the brochure. Without this coupling piece, they can't imagine combining the parts because the interface on both would have to be messed with. Between article number 4711 and article number 0815, adapter 333 is needed, otherwise the warehouse computer won't add the order to the shopping cart. Without adapter 333, articles 4711 and 0815 would have to be modified, which would result in costly individual planning. Logistics merchants – what they lost in construction: don't ask me. Henry Ford's Tin Lizzy could only be bought in black. Allkauf Haus is not a Viebrockhaus or Weberhaus.
I'll be honest: it has improved, but there are enough indications advising to take a blank sheet of paper and plan some rooms differently.
But now the course is set – a purchase contract with a catalog manufacturer can't be changed so far that you'd end up with an "architect's house."