If you fly business class you get waited on hand and foot the whole time, get plenty of space to lie down and sleep, and a reasonably quiet environment. On the next step up (ie not spending millions and millions of dollars on your own plane), you’ll be on a much smaller (probably noisier) plane with fewer comforts (you’ll likely be back to sitting instead of lying down), worse food, fewer supplies of things you might want to ask for (that you didn’t specifically request in advance of the flight). Depending on how your flight is organised you may also have stricter scheduling requirements (maybe you could turn up a few hours early or late but maybe you couldn’t rebook your ticket for a different day). And for all that, you’ll pay a lot more.