Retired patent attorney here. It boils down to a) sufficient pain; and b) cheap-enough way to make that pain go away that people will actually pay for it. Lots

Retired patent attorney here. It boils down to a) sufficient pain; and b) cheap-enough way to make that pain go away that people will actually pay for it. Lots of reasons not to have wheels on luggage: 1. they stick out, making them tricky to put into overhead compartments; 2. they need a certain degree of durability, while rolling; 3. they need a certain degree of durability, when getting smushed together in a trunk, compartment, or baggage-handling carousel; 4. they can't be too expensive/complicated, or part 'b' isn't satisfied. Consider, also, that its only been the last 10-25 years or so that virtually all parts of grocery carts could be made 100% from durable plastic, and still hold up (and I'm still uncertain that no metal is present in the axels/bearings). Further, there are lots of weight restrictions, which heavier bags (the 'shell' if you will), necessarily impinge upon.