You're absolutely right it's worse than a local place. But it's predictable.
It makes the process of choice easier: I can go to McD and I know what I'm getting or I'm trying this new place, with unpredictable results.
Starbucks coffee in Japan isn't great, but it isn't fucking gross either. And it is very, very consistent.
Not necessarily having to do with the predictability of the coffee or the experience of drinking a coffee in a place.
I made a real effort to go to the local places, but they just don't offer what I need. In a Starbucks you can come in and sit for a few hours reading magazines, studying or working. Nobody bothers you. The place offers a variety of couches, chairs and tables which you can pick based on what you plan on doing. In a local cafe once you're done with your coffee or tea you get pressured into leaving by constant questions about your other orders. Local cafes offer uniform seating which often is completely unsuitable for a laptop or a stack of books.
Starbucks is a good Wi-Fi provider, worldwide.
But before this, you could see poor quality local food places on highways. McDonalds and co came in and create a price/quality floor. You couldn't be worse than them.
How do you get scratched DVDs from Amazon? I didn't think it was possible to scratch a DVD inside its case, without literally crushing it to splinters.
In that case, excellent online stores would sell the items in a separate category at a reduced price.