A case of social engineering.
The espresso machine was pioneered by entrepreneurial Italian engineers, they innovated the concept of forcing the water through the coffee grinds and washing out the coffee oils. It was a new method for consuming cheap coffee. With the introduction of the espresso machine they found it better to dark roast, that is they roasted all the natural flavours of the coffee bean (if it had any) up the chimney (if the bean started with any) and replaced them with the toasty notes from the roaster. They found this caramelized the sugars more and that cheap coffee tasted pretty good. Especially if the bitter sweet notes were extracted in the shot.
There is no purpose in dark roasting an expensive coffee, one that has to be found and searched for like treasure, you want to retain those complex tasting notes that you have travelled around the world for and suffered the wretched cramps as you throw your remaining green bile up or sweating it out on a stained and stinking mattress. No, after that, I am going to retain the flavours, so I am going to lighter roast to maintain as much of the character of the bean as one can.
A good cheap coffee, on the other hand, you can darker roast and get a significantly better body because the darker roast breaks down the organic matter of the bean to make it more soluble. The darker roast means the beans are more brittle meaning the grinder the blades can be closer together to grind the beans very finely. The intensity of the pump pressure forces a specific dose, of very hot water to smash the bed of coffee and in a dream like wave pass through the bean absorbing and sucking its total inners. The inners includes the dissolved bitter sweet complexities of caramelized sugars and its tasty provided in a heavy coffee to water ratio. It's coffee extract. Its body.
Espresso coffee is about the body of the coffee more than the flavour. Well, it's at least 50%. Even with milk an espresso shot really enhances the fine foamed and shining body of a well prepared milk. It's a perfect breakfast in itself.
Espresso is about good body, flavour diversity is secondary to the body. Sure , as long as it's good coffee flavour. Your not that concerned about flavour complexity, there is not that much of it with espresso it's all bean roasted out. There's just a few roast and blend styles for espresso, wine's divergent complexity outshines espresso along way in comparison. But the body of a good espresso wins hands down over any glass of wine. It's incredible not only in its viscosity but its secondary kick and lingering film. This is what the espresso machine was made for, this body and taste hit. It was new and much more sexy than carbonated sugar water. But for all historical culinary purposes this was a beverage of the new industrial worker in Northern Italy. A great natural man made beverage that had not been bettered since its invention. It was the morning way of great quaffing wine. The espresso machine gave consumers a different style of coffee using the same cheap stuff. Espresso coffee came about because Italian industrial engineering entrepreneurs were smart and wanted to make money from cheap coffee.