you meant a seam between the two parts.
While I think the seam can be minimized by a more precise machining/manufacturing process, I think it will come at a cost of:
Increased number of sharp edges (due to the need to keep the “mating surface” as smooth as possible, thereby disallowing chamfer/edge blend)
Reduced ability to open up the laptop cover (might need suction cups)
Increased cost (due to increased precision)
While it’s possible for this “seam” to be hidden elsewhere (e.g. the palmrest surface), basically all laptop have a seam and I think it’s not a big deal. It’s almost completely irrelevant, in fact.