Why do I always get stuck for hours at O'Hare?

Blame the major carriers' hub and spoke system. This and other interesting factoids are discussed in an article by economist Austan Goolsbee. He does a nice job articulating why I fly on Southwest out of Midway (Chicago's other airport). Excerpt:

American Airlines, for example, uses O'Hare as a hub and schedules a cluster of flights to arrive there from the east in the earlier afternoon. Another cluster leaves for points west and south soon after. In the 30-minute period between 2:45 p.m. and 3:15 p.m., American has scheduled about 18 takeoffs, not counting its regional flights. That comes close to maxing out the airport's capacity, without any other airline. Other airports are even more extreme. Continental has seven flights scheduled to depart during the exact same minute (11:45 a.m.) out of Newark, as well as almost 20 other flights in the surrounding half hour. Some of these flights leave late more than 80 percent of the time. The major airlines know perfectly well that these hideous statistics are inevitable.