For those staying on site, WDW was designed so having a personal car would not be necessary. With Walt's love of railroads and of futuristic things, the monorail was chosen as the transportation between resort and park.
Walt did not live to see even the first park open. With the opening of more resorts, it became clear that monorails and private cars would not be able to reliably handle the guest traffic at reasonable cost. (You know about all of the monorail breakdowns, no?) So WDW did what any big city would do, run a bus system.
The transportation & ticket center was to give guests the illusion of transitioning from the real world into a fantasy world (and back to reality at the end of the day). But bringing all of the resort guests there to ride the monorail or ferry to Magic Kingdom would overload those facilities. Also too many guests want a more direct trip to Magic Kingdom although it was too late to reconstruct things so guests driving could avoid the TTC to MK link.
Who remembers that Walt's original design for Living Seas was a base deep down under the sea and "hydrolators" would "transport guests down and back up". Long waits for the hydrolators were common. Partly to improve guest traffic flow, the attraction was rethemed to be "on the surface" and the hydrolators, which really did not go anywhere vertically, were replaced by a straight through corridor.
Who would be in favor of covering all of the bus windows and have decorations and maybe even have several video screens all along the inside walls, to provide a more magical trip from resort to park? This way guests would transition from the real world to a fantasy world upon arrival at their resorts.