The same hubris that powers faulty and half-baked implementations is responsible for lying to regulators.
The problem here is that Musk isn't really a humble man, and he's the face of Tesla. That makes everyone a little on edge. Of course, there's a lot of other people in Tesla who, I'm sure, are fantastic engineers and designers. But still, the feeling of uneasiness ensues.
If companies want to earn the trust of the public, they have to anticipate our questions and concerns and address them. It's a high bar in modern America, which is why so many industries (food, pharmaceuticals, automobiles) are plagued with low-trust.
The ensuing cover-up attempt wasn't, though.