I think it's the Starbucks mentality. Do you want to risk getting a bad cup of coffee at a place you know nothing about, or are you going to go to a chain where you know what to expect?
Even if I personally do not care for the taste of Starbucks coffee and would rather support somewhere local and risk getting a subpar cuppa, other people default to the safe choice.
'"Contrairiwise," continued Tweedledee, "if it was so, it might be; and if it were so, it would be; but as it isn't, it ain't. That's logic."'
~Lewis Carroll