Timing, cost, and marginal return on investment of effort. Timing: When you check your bag, it travels with you. As a result, it arrives at the same time as yo

Timing, cost, and marginal return on investment of effort. Timing: When you check your bag, it travels with you. As a result, it arrives at the same time as you. It also spends the minimum amount of time outside your possession. These two traits are desirable to travelers. Cost: If you were to ship your bag, most travelers would need overnight service, because travelers simply don't pack two or three days ahead. The cost of shipping your travel supplies overnight isn't going to offer a cost advantage to the $25 (estimated) it costs to check your bag. Marginal return: Yes, it would be possible to plan ahead and ship your bag through a parcel carrier's ground service, but depending upon where you're traveling to, that can take 5 days. That's a lot of planning, and the marginal increase in risk (of lost baggage) doesn't offset the time and effort required to "optimize" against this risk.