I think you are missing the point.This is true. Oftentimes the additional cost and reduced spatial efficiency of parking lot systems are overlooked for the added intrinsic value from putting a system in clear view of customers plus the shade provided for parking. If Disney were doing this simply for PR they probably would have looked harder at a parking lot system. As someone mentioned they could have charged a premium for shaded parking. Hell, they could have used it as a justification for increasing the parking fee by $1 and funded the entire project with that extra revenue.
The decision to do a system on open land alludes to the fact that they are always looking at the bottom line and that this was more of a $ decision than PR, which we all know is what TDO is really paying attention to.
While making a dedicated off site solar farm will cost less than trying to incorporate it into a parking lot, it is without question the better way to do it if they are serious about actually generating power and not just doing it for appearances.
This is not TDO being cheap, this is them doing something that actually works.