This is a conspiracy theory. The other part of the story is that if the streetcars were a better investment, General Motors would not have done this. Streetcars are slow, inefficient, and require rail lines to move about. So, if these companies realized the assets they were holding, then they have the opportunity to get rid of them.

If you were an investor, the up and coming item was streetcars, as the article mentions they were better than horse-drawn carriages, so taking a stake in these would have been a good idea. The article mentions that the transit systems are expensive to maintain; as publicly held companies, they need to make money. The current day transit systems with rail lines are heavily underwater and have a difficult time making any money, let alone addressing maintenance issues: BART, Metro, and Max. Knowing the return on investment from existing data, would you as a private investor purchase any of those lines.

So, the conspiracy can be developed in retrospect, but an over arching plot fails to account for some of the opportunities that fit more into an investor trying to make monies.