Nothing to do with greed, just allocation of pricing to socially engineer its guests and get the expected outcome that they want. Trust me, a corporation is as aggressive as it can be with prices, don't worry about that. If they wanted to give away free parking, and make wash and wax your car for free too, they can and will... but you'll never an uptick in everyone's ticket prices, or they'll tack it onto the price of the hotel.
Think of it as you requesting for a reimbursement to park, and the park preferring to give a discount to those who can find other ways in. You can probably imagine that Disney does not keep enough parking spots on campus (including the resorts, hotels, waterparks, water treatment plants, parks, corporate offices) if EVERY park guest, employee, and contractor drove their OWN car and expected it to be sheltered by the park. So as an incentive to minimize the risk of running out of spots, you give people a reward for carpooling, taking a bus, Ubering, walking, etc. by not paying $25, and in the case of carpooling, only paying $25, and not paying her person.
Obviously in the case of the hotels, its the same logic. They're more than happy to accommodate your car, but they're much happier with you if you find a more practical way to get to the park.
One of the most precious economic resources that we have is land -- maybe the most precious resource. Disney could buy up more and more land around it to accommodate your precious cars, but that would be difficult and prohibitive. Plus, parking lots filled with cars are kind of ugly -- it goes against the image that it wants to portray.
So that's my lesson to you on why its important for parks like Disney to charge appropriately for the privilege to park.