Starbucks changed coffee for much of America. Before they spread like the plague coffee was mostly worse (depending on your taste, but decidedly better than Folgers there is room to debate the merits of diner style coffee). They ruled the roost for a long time and people got really used to drinking that which they push. What they push is blends that have little distinctive flavor. It's really hard to provide a consistent cup of coffee with distinctive flavor on the scale they operate, probably impossible (Same coffee plant on different sides of a hill will taste different). They blend a bunch of coffee together to make a pretty muddled average tasting coffee and then burn the shit out of it. Brewed charcoal has an amazingly consistent flavor profile! It's less bitter and acidic than the coffee people two generations ago drank and it's probably the best coffee you can easily get your hands on in most the country.
Starbucks doesn't sell a lot of straight drip coffee. They sell a lot of milkshakes with a bit of coffee in it. They sell a caffeine sugar rush with slick marketing. They pay reality show celebrities to hold their cups logo side out on their Instagram accounts. People drink Starbucks because they identify with the brand and like how caffeine and sugar make them feel. Starbucks moved in two blocks from my shop, it made no difference in my business. A few customers probably went to them for their coffee milkshakes and a few new ones checked me out to spite Starbucks. Starbucks is right down the street selling a lifestyle and I'm over here selling coffee.
Most coffee is mediocre because making good coffee is hard work. I do very little of that hard work, my roaster does a lot of it. He tries a shit ton of coffee, he has two buyers who try more at different ports. Most my coffee comes from one family, farm or co-op. Each coffee is a unique product of how and where it was grown and processed. They pick a few they like, buy up what they can, run it for a few months and hunt up some more. My roaster has 5-7 pour over coffees on his menu at any given time, they are all distinct. I guarantee that I'd hate at least one of them and that someone out there loves the one I hate. How he roasts it is a whole other ball game. A coffee can bit brilliant or horrible depending on how it's roasted. The way he roasts for the brewing equipment I have is different from the way he roasts for the equipment in his shop.