Bringing the goal posts back to the original aim of my comment: that a DIY community would simply increase adoption, let's look at the Tiny House movement. It grew as a DIY community. People sharing info on all parts of the process, incl. building code, helps many people who would have been told by someone that it can't be done, just as you are doing now, to build their own house. And we are talking about building an entire house, not a minor solar panel install.
As that community grows, you have more people that are able to even shape laws for the better, which is what that community is doing.
And you are incorrect about there being no laws governing auto work and customization.
No one is saying you should do this. To be frank, the "hire a qualified contractor" advice is pervasive at HN, but it's also this groupthink attitude of negativity that can grow around a subject that I don't think is necessary, or helpful.
Because if you're breaking building code, you're breaking the law. That's the entire reason the Tiny Home movement has to build their structures on RV trailers; to be compliant with building code (which doesn't apply to RV trailers).