If I want squeaky-clean glasses, I clean them by hand so I can't say that I relate to your experience. Perhaps the dishwashing detergent that you use contains different chemicals.
Might also be because people misuse the dishwasher a lot - by overloading the machine past capacity, and then running an underpowered (or "eco") program. All those other programs are on the dishwasher for a reason, and it's not to trick the user into wasting more water.