Ot has nothing to do with travel patterns for many people. You can use the Starwood Amex to earn points to transfer to miles without ever ever ever setting foot in a Starwood hotel. (Since you're going to use the points for miles, you don't care that you won't redeem in a Starwood hotel. And Starwood doesn't require you to stay to earn miles or keep your account from expiring, just earning or redeeming "activity" which you "automatically" get if you're using the Starwood Amex most months.)

It has to do with a preference for miles vs hotel points. If you want miles more than anything, Starwood Amex could make sense for you no matter where you tend to stay. It's only, presumably, because you want every last spend to be going to your preferred hotel chains now (and don't care that none goes to miles) that it doesn't make sense for you...