They’re different tiers, but economy is the majority chosen due to the price (business is expensive for most travelers hence why they opt for economy even if its crap) and it depends on how long the flight is rendering the price difference justified. If on a short flight, then economy is ideal if on a budget. However, if you’re heading somewhere it’s distant: business is better at the expense of paying a lot more than economy.
I deal with economy on the flight to Japan, but my last time coming back, I bought the upgrade (work paid for the base fare) and being able to lie flat and actually get some sleep was a game changer for getting back on US time. That said, I got an incredibly good deal, and have to face the fact that I likely won’t get the upgrade next time I come back to the States.