I don’t see why you would think that. Someone like Bernie was too radical for the American left to win a primary, no way he would be considered more appealing to America at large in the general.
It’s frustrating because Biden/Harris are too moderate to capture far left voters and too radical to wrestle the center from a populist like Trump. And it seems many disenfranchised voters are content to stay at home because better isn’t good enough. I’m not trying to absolve them of responsibility, but I genuinely think Democrats could make great strides if the left was as good at banding with each other as the right. Instead, the Democrats lost the popular vote for the first time in twenty years.
The obvious answer is that it’s fast, tasty, and requires minimal effort for the consumer, especially if it’s getting delivered. But it also tends to be very cheap compared to dining out. I don’t know what you are ordering where a combo is so much but I normally get a bunch of food from Taco Bell to eat over the course of two days. I can get 2000 calories of food I like to eat for $12.