I’m reasonably sure [B][I]levitating [/I][/B] trucks have not in fact been invented yet, but a garbage truck (levitating or not) is offline for at least 16 of 24 hours, in a location mechanics would have access to it and be able preform routine maintenance and repairs.
A ship on the other hand must operate 24 hours a day for several days in a row, and then be shut down for remarkably short periods of time, big difference.
You seem overly sold on the promises of “gee-wiz” technology, people with real world experience tend to be far more skeptical of “foolproof” unbreakable machinery.
Perhaps less time in an ivory tower and more time in a ship yard or at sea would provide you with some insights.