Why do the tubes in the Seattle Space Needle Architecture set need to be cut?
This happens in Technic models as well, at least for pneumatics tubes. I would tend to assume it's a simple production issue or simplification - as this requires less work from LEGO.

That way, they only need one length of tube per model, instead of having one part ID for each of length of tube. Considering LEGO wants to control its number of elements currently in production (it's not infinite), this makes sense.