[PinguTS]

Because of economics of scale, you design one versatile truck chassis. That can then be easily modified like longer vs. shorter for the super structure, the driver cabin is modified in size so that you have a sleeping possibility or not and all those things.

Just take a look, the very same long haul truck is also used by the construction workers. Only the the cabin is a little bit shorter.

[eloisant]

That's true when you're big already like Iveco or Caterpillar, but when you're trying to enter a new market it makes sense to cater to a specific subset of the market.