Several factors have contributed this
I lived in DTLA for a long time and I didn't have a car, because I couldn't afford one. I relied on my bicycle and public transit to get me around. It wasn't too bad for me, overall, except when I had to travel to a place like Orange County, because they didn't have a light rail system, and the bus system was great. I took full advantage of the blue, red, green, gold, and expo lines. I HATE riding the MTA buses. Blue buses, Long Beach Transit, and OC transit were okay rides. Sometimes the trains were crowded...especially when school was in session, but most of the time they were not bad. The light rail system in LA has gotten much better, however it needs improvement, and OC needs a good light rail system. With that being said...why do American dislike mass transit.
I can only speak on my experiences with public transit and they're limited to Southern California and NYC. The problem IMHO with public transit is the fact, that bus lines are often crowded, and the people in Socal are used to being in their cars. The culture in Socal is centered around the automobile. Yes I know that was done on purpose by the oil companies back in the 40's and 50's. It is what it is. The problem in LA is the fact that the trains and especially the busses are crowded, as in sardine can, crowded, to where you have to fight your way through the crowd to get off on your stop. The other problems for me at least is waiting forever to catch a bus on certain routes...especially on the holidays and weekends. On top of that, dealing with the homeless on the bus. I'm not getting into the reasons why they're homeless, but I will go into the fact they had bad body odor and carried diseases. I got staph sores on three different occasions, because I let a homeless person sit next to me. There were also people on the bus that want to start fight. One even started a fight with me and bit me in two different places, but that turned out to be a good thing in the long run, because it gave me a moment of clarity and caused me to reexamine things. I was constantly on guard and that contributed to my heart attack in 2018. Needless to say I was living a warzone. I didn't have any problems with NYC subway system.
I liked using the subway system in NYC, because I could get to just anyplace in that city via the subway system. I lived in Hackensack NJ, and I would drive my car to Jersey City, and park it there, then take the path to the city. It was pretty great, because driving a car in NYC is a nightmare. I'd rather take the subways, and walk a short distance to my destination.
Mass transit in certain places is a great idea...like LA, but there needs to be more light rail service in that city, in order for it to be effective. Mass transit isn't practical where I live at now, because its a rural area, and there's no way I can bike from eastern TN, to Asheville NC, to get to my doctors appointments. A lack of personal space, is probably the biggest reason why public transit hasn't taken off in the US like it has in other parts of the world. That, limited funding, and the fact that American has been steered (pardon the pun,) into a culture that's focused around an automobile.