Balance is a big reason.
Ship attributes are arbitrary. There is no coherent system behind it and no internal consistency, never really has been. It's not like reality, or Space Engineers, etc, where the constraints of the underlying systems enforce a balance of their own, so they have to be individually balanced against everything else...which hasn't been going well with only the ships they've got.
The game also has many other areas in need of attention and selling broken ships for a broken game may well not bring in enough revenue to justify the effort.
Ship attributes are arbitrary. There is no coherent system behind it and no internal consistency, never really has been. It's not like reality, or Space Engineers, etc, where the constraints of the underlying systems enforce a balance of their own, so they have to be individually balanced against everything else...which hasn't been going well with only the ships they've got.
The game also has many other areas in need of attention and selling broken ships for a broken game may well not bring in enough revenue to justify the effort.