Because a majority of the flights out of your home airport are run by them, and it's a connection to get anywhere else? That's my reason, although I take Delta to ATL, United to ORD, etc., when I can.

Free flight to over 600 destinations, Sydney, Athens, Bangkok, etc.... as long as you book a Wednesday departure double redeye with layover, 330 days in advance, and are flexible about your return week.

Just try getting somewhere you actually want to go, when you want to get there. It's difficult but sometimes achievable on US, often not so on the great *A network. I'm actually contemplating using miles for my family on a $200 PIT-BOS flight over Memorial Day - I never would have even though of redeeming at <1cent/mile a couple of years ago, but now they are a greatly depreciated, and depreciating, asset.

But I'll still fly them over the WN cattle car. The free upgrade do still have some allure. I'll see if I still feel that way after my first non-CP year in a decade. Only 26 days left....