I don't think Tesla is the kind of company that can handle building a car like Model X without significant quality issues.
And, judging by all the other companies that make complicated, fast, expensive large vehicles, nobody else really is either (BMW I'm staring directly at your turbos and wastegates and fuel systems and cooling systems and window regulators...and rod bearings and electric water pumps and ok maybe they'd be pretty good if they just made EV's). Body and trim is hard to get right, and it's where the humans interface with the car, and Tesla doesn't do it well enough yet on the X and S. It makes sense they'd get good on the 3 and Y first, they've made a lot more of them and it's a much less complicated car. Which is a good sign.