While it is seductive to think we can 'just let the market take care of our transportation problem' but business realities make this approach impractical.

Problem 1

Building a new mass transit system in a medium size city (the Tampa Bay area for example) will take capital expenditure over several decades.During that time period the business is unlikely to be making any profit. Business that lose money for decades don't stay in busineess.

Problem 1.a

Building a new mass transit system will require a very significant taking of land. (I know you can tunnel but it cost a lot more and in some settings it is cost prohibitive.) Lots of land will need to be taken by imminent domain. Giving (or leasing) land acquired this way to private companies is fraught with both legal and political problems.