People could get by with a much smaller salary (or keep the same salary but save a ton of it) by having an older car, a smaller house, less fancy food, etc. but everybody else has nicer things. I see people buying really nice cars on credit and then they don't have much time to drive it recreationally because they spend all their time working to pay for it. "Well there's your problem!"
For the other side, let's say I make $X but only need $X/2 to live. Try finding an employer who will let you work half time for $X/2. It's pretty tough, especially if you make $X at something "professional", rather than, say, digging ditches. Worse, for Americans, is the current link between employment and health care. Half-time employment generally means having to buy your own health insurance, which doesn't come cheap.
In short, it seems like it's pretty hard to work less and make less, and when you do work full time and make good money, it's very tempting to spend a larger portion of it on luxuries.