People prefer how it looks and it's also more convenient to have a square room and no irregular protrusions stopping you pushing furniture up against the wall.

In the UK it used to be common for pipework to be exposed and painted. Electrical conduit is pretty common in "industrial" places like garages but the number of sockets people expect now would mean you'd barely have a flat wall anywhere.

The current preference is definitely for clean looking, square rooms. When pipes don't fit in the walls themselves, like soil pipes or around boilers, they are boxed in or hidden away in a cupboard.