It varies by the locality, but the municipal inspectors in the US often let you get away with doing your own electrical and plumbing. They come down harder on gas, though. For a pretty sensible reason. If you mess up electrical or plumbing, you tend to only fuck yourself. If you mess up gas, you tend to fuck your neighbors, too.

I can. I'm in Portugal and we can fix things in our own house, except for gas and appliances like AC.

Insurances only care what you do when it damages others. Like a pipe bursting and flooding your neighbours house. The burst pipe needs to be fixed by a certified worker but whatever it may have destroyed in your house you can have it contracted or fix it yourself. Or not at all. You only need to provide a proforma invoice for the work and materials, by a professional. If you fix it or not, that is your problem.

Electricity is a touchy subject but you can modernize a house entire eletrical circuit by yourself and only pay a professional to inspect it and have it declared as up to code. And it is not that hard to make things better than professionals. You already know the reigning logic.

Inside buildings, it's harder to perform work on water and sewer lines but you can renovate/improve anything up until you reach the main pipe, which is common property. I have a stand alone house and I'm forced to do all of these works by myself because I have a mess inside the walls and ground, for water, sewage and eletricity, because nobody wants the job as I want it done.

And connecting modern PVC to 70 years old ceramic pipes for waste water is not safe nor adequate on any level, yet...

And me wanting a properly done breaker box, with separate lights and outlets for each room is too much of a hassle.

I'll go complain to my walls, as usual, and take my leave here.