One of the reasons, is believe it or not, but motorcylce riders are much more of an interest group than automotive enthusiasts. What I mean is that they are very political, usually a lot older with much more money, and invest heavily into people pulling these laws into their perspective.
With auto enthusiasts we seem to only have manufacturer's and a group like SEMA fighting for our rights or what we want. Motorcyclists are seen as a seperate group while automobiles are driven by the majority and not just a small group, so when laws are made for cars/trucks/suvs, our politicians think they are only saving mom carrying her four children to their soccer practice games and not auto enthusiasts trying to make their cars a mix of science and art. When it comes to cars we pay more taxes than the mom in her minivan filled with kids, we've brought up the aftermarket business into a billion dollar industry, we buy tires more, we upgrade everything we can. Until we as auto enthusiasts can come up with something like Boston's Tea Party, I doubt we will ever be heard.
In New Hampshire, if you're over 18 you don't have to wear a seat belt, what's interesting is NH car insurance is much cheaper than most states that have very strict safety auto laws.