GM Comes a-knocking...
http://en.wikipedia.org/wiki/General_Motors_streetcar_conspiracyThe first and most voracious was a targeted campaign by GM and other car/tire manufacturers. Car companies created dummy corporations, and bought out local rail companies, along with their tracks. Then a few years later they would close down the rail line, and sell off the equipment, and make a profit off of the former right-of-way. That and other factors resulted in a dramatic increase in sales of vehicles. This corruption made some politicians rich, and robbed everyday people. A court case was even brought against the car companies in the 1940's and 50's. They were found partially guilty, but ended up paying a very small fine for their actions.
Robert Moses...
http://en.wikipedia.org/wiki/Robert_MosesThis had a ripple effect. Engineers who worked with Moses went on to other posts in other places, and city planners ran with Moses' model, and began working on other cities, ramrodding massive highways through downtown areas, building ever wider roads. The national highway system gave massive amounts of money to states with new Highways construction, so of course the incentive for public rail systems all but disappeared.
Economic Change.
The 40's and 50's saw the rise of advertising. The median income rose dramatically. For the first time, people had more money to spend on transportation. Meaning they could afford cars, and not the small 4 bangers like the model t. No, the cars of the 50's and 60's were larger, heavier, and needed a lot of parking space. Add to that mix low gas prices, and the flight from the problems of the inner city.
What changed?
http://www.theatlantic.com/business/archive/2013/02/the-american-commuter-spends-38-hours-a-year-stuck-in-traffic/272905/
But then engineers took a look back. Trains allowed for maximization of transit routes. You can fit thousands of commuters through a train artery for every dozen cars. Allowing consumers a variety of commute options lessens' traffic, increases density and reduces the strain on already strained roads. Ultimately they help to move more people faster and for less, and help to build a tax base. People move to where the stations are, and businesses follow them.
That's why local commuter rail makes sense... and why its resurrection in Central Florida just might work.