Lol, of course the Enterprise wasn't made to fly in the atmosphere, but here's the description from the writer's perspective on the Enterprise being constructed on Earth: "One example of a concept which seemingly contradicts
Star Trek canon but came from the precedent set in the novels was having the
Enterprise built on Earth, rather than space. Orci said that the idea that some things have to be constructed in space is normally associated with "flimsy" objects which have to be delicately assembled and would not normally be required to enter a
gravity well. He said that this did not apply to the
Enterprise because of the
artificial gravity employed on the ship and its requirement for sustaining
warp speed, and therefore the calibration of the ship's machinery would be best done in the exact gravity well which is to be simulated."
That's enough for me lol