You can also have even faster at home or at work - and at no cost. It amazes me that people "grab Starbucks on their way to work".

Yes, but that's less convenient. At home, anyway, you have to make it. That's more effort at a time when many are in a rush to begin with. You can have it at work, but many prefer to have some coffee a bit sooner than that and not have to make a trip to the break room.

Convenience is a very powerful motivator, and these people are prioritizing it over minimizing monetary expense.