Because then pretty much EVERY insurance company will pick up and move to the one most desperate state that writes laws in their favor, doesn't tax them, allows them to sell substandard insurance, gives them liability protection and forced arbitration and in every way abuse the customer.
And the industry will become abusive, fraudulant, manipulative, and untouchable. Every state will lower its standards and revenue streams to keep insurers from leaving and taking jobs with them. And the customer will have very few if any good choices and no recourse when screwed over. Over time, the industry's power over the state will become even more entrenched. Exhibit one: The credit card industry, and south dakota. Go watch the Frontline episode I refer to in another thread.
I'd like to answer some of your other questions like "why do I have to buy a plan that covers obgyn" but I'm too pissed over having to pay for rear seatbelts I'll never wear, a space program I'll never use, fire hydrants I'll probably never need, and taxes for schools I'll never attend. Living in a society sucks. I mean, I have to pay for roads I'll never drive on. It's bullshit. I mean even my freaking insurance-- I have to pay for all these diseases that it'll cover! I'm NEVER gonna get ALL of them at once. And only one of them can even possibly kill me, maybe two max. Why should I pay for protection from a heart attack AND cancer treatment?!!! Bullshit, man. That's how they get you. I mean, I saw tonsilectimy on the list and I don't even have tonsils any more. Tyranny. I want an a la cart health insurance plan where I can figure out what I'm likely to get and only get insurance against that specific disease!!!