Well, first thing - Disney is not actually IN Orlando, Orlando is actually north of the attractions area, and has quite a bit that is not tourist oriented - Health Care, Lockheed-Martin, IT, etc. Of course, the HSR proposal only connects to the convention center and airport (both essentially attractions area), so there is definite need for another connection to them. Hopefully they will end up connecting SunRail properly.
But from a scale perspective, Orlando and Tampa sit at just that right distance that is too short for a plane, but an awful long drive. And Lakeland happens to sit along the perfect line between the two. This isn't going to necessarily be along distance HSR route, but it is long enough that there is a time advantage over convention rail.
What most tourists see of the two cities is not what most residents see. In Orlando most people rarely venture out of LBV/Kissimmee - Downtown Orlando is pretty centralized. And there are some developing urban centers. Likewise, Downtown Tampa is pretty big, but centralized enough that there is a downtown. Most people never get to it, though, since they usually stop at Busch Gardens. But Tampa already has a streetcar, even if it only really serves as a tourist line.
But the point is, that you have an overlay market. On one hand, you have some big tourist attractions along the way and at the end points. But you also have two urban areas that could easily be connected as well. And, you have a nice residential feeder system as well. The tourists are going to be the ones who need the transit at the ends. so long as the HSR line connects to the business districts as opposed to the outskirts, then commuters are going to drive to the station, and then get off at work.
I think a lot of people are assuming that people will drive over take the train if all other things are equal, but that's usually not the case. People would actually rather be on a train where they can work or read or rest instead of having to put up with traffic if it gets them there in the same relative amount of time and schedule. That has been proved out by many commuter rail systems already.
