It’s clear that, as between San Antonio and Chicago, San Antonio has more U Haul trucks than it needs and Chicago has fewer. What other likely explanation could there be than that, controlled for population size, comparatively more people are moving into San Antonio and out of Chicago?
Update, March 9, 2016:
Powerlineblog reports on a similar phenomenon with California. It’s cheaper to rent a truck going there than to rent one leaving. Steven Hayward suggests an unfriendly tax and regulatory environment and notes that, as businesses’ lease obligations expire, more might move.