The 10th amendment to the Constitution reads "The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people."
I'm seriously questioning the absurdity of banning something that remains available a 15-minute drive away, behind a purely informal border. I don't think, for example, that recent abortion bans had reduced the number of abortions in their respective states to zero.
1) For the vast majority of Californians, the nearest state border is 3-5 hours away. 2) those abortion bans have definitely reduced the number of abortions. Not zero, but that's a silly goal for any ban.
Obviously the law is stupid. But states passing their own regulations isn't on its face.
About half of Americans lack any access to intercity transport that isn't a private car.[1]
About 15% of rural Americans aren't within 25 miles of any intercity transit, much less interstate; low-income residents are disproportionally represented in that group. That figure jumps to 25% if you exclude suburbs, and in some states that figure is as high as 62%.[2]
Even as intercity bus demand has increased due to the declining quality of air travel in the US,[3] rural intercity bus access has declined. Greyhound served many rural routes until its slow collapse before being acquired by FlixBus, which is more focused on urban access than Greyhound was. The deregulation of intercity bus access in 1982, which led to the closure of many intercity routes (disproportionally in the rural Midwest) that required subsidization from more profitable routes, was a major factor.[4]
So "what percentage of Americans can't afford a bus ticket to the nearest city in an adjacent state" is a non-starter of a question, because most of the Americans who'd _need_ an interstate bus ticket can't even get to a bus stop without first owning a car... with which they could simply drive to another state.
A lot of rural areas don't have good transit. Even if they do, it's hours round trip. Here's an example. North Dakota has an abortion ban. Someone in Minot would need to travel almost 5 hours to Moorhead, MN or almost 7 hours to Billings, MT. Now that's not any different really than before the ban, because the only clinic in ND that provided abortions was across the river from Moorhead in Fargo. But what if that clinic in Moorhead closes? Or what if Montana bans abortion? It's banned in South Dakota, so people out in western ND, SD, or anywhere in Montana are going to have to travel even further. There are many small communities around here with no bus lines or trains coming through so they're stuck if they don't have a good car.
California has a huge influence on the American economy. When it makes a law, companies and other states pay attention. The farmers, senators and representatives in my state, Iowa, are still wringing their hands and pulling out their hair over California's law which "unfairly" manipulates the hog market by requiring all pork products sold in California to come from pigs which are humanely treated according to California's definition of humane.
US states aren't as small as you're imagining them to be. Almost everyone in California lives more than 15 minutes away from the nearest state border, and the largest urban areas are 3+ hours away.
Procedurally the US is closer to a EU style alliance of sovereign nations than a single one. Practically the federal government has long since overgrown it's constitutional role as the equivalent of the EU bodies but if you're looking at a US state and wondering why it's acting like a sovereign nation the answer is generally because it is one, on paper.
Assuming this is a sincere question from someone who doesn’t know US history:
States in the US were modeled after sovereign nations, perhaps even more loosely connected than the EU is today. They didn’t even share a currency.
Eventually the federal government became more important and powerful, and there are many federal laws now, but states are fundamentally still their own thing with the rights to do certain things that are more like a sovereign nation than a province.