This is a guess from a non-lawyer who took a business law class a long time ago in a different state:
I think it's like the UCC (Uniform Commercial Code). It's a set of laws that were written up to be pretty much universally applied anywhere and there's a push for law harmonization that has resulted in legislative bodies (state legislatures in the case of the UCC, City Councils in the case of the IMC) adopting it verbatim as the law of the land on that subject.
If you're in the USA and you're doing business, it's probably under the UCC, because your state has probably adopted the UCC in its entirety as the law of the land regarding business law, contract law, tort resolution, etc. If things come to legal unpleasantness, it still means that you need a lawyer admitted to the bar in the state where the complaint is filed, but it also means that if you're in state A doing business in state B you're generally bound by the same legal framework of commercial law, so your standard contract boilerplate works nearly everywhere. Last I checked, Louisiana was still operating under a weird mix of the Napoleonic Code, English Common Law, and the UCC, but most other states have adopted the UCC entirely.
The problem with applying the principle of uniform laws to municipalities is that towns (or even neighborhoods) aren't all the same, don't all have the same interests, or the same sort of people with the same concerns. It's stupid to assume that one set of ordinances will fit all municipalities. But then we have lots of elected officials doing stupid things for selfish or just plain stupid reasons. I know for a fact that there are companies that draft these things and sell them to development companies (for HOA bylaws) and municipalities (for zoning ordinances). You can bet that they're placing full-page ads in 'local government today' or whatever to sell the idea of standardized municipal ordinances.
And that's why I'm on the top of a hill zoned rural (and likely to stay that way because they're not going to run municipal water and sewer up our cliff of a road to serve 60 houses).