That's because flights from hub airports tend to be more expensive, and therefore a better value when using most airline miles. (creditcards.com)
In addition to looking beyond the big airlines when you're traveling, another good tip is to look beyond the big hub airports, too. (cheapticketlinks.org)
One of those visits was a chain in airport duty free shops, which had outlets in hub airports in New York, Boston and Philadelphia. (canadianbusiness.com)