[distances]

That's because it's expected, all their friends are living in the same way, and they see this as temporary, with a larger income not that far off.

I can say I was very happy with minimal income in my university years, but would not be anymore as my friends are out of the campus and getting forward with their lives.

[aianus]

Yes, so it is not the lack of money that makes one unhappy (say, at ~$24k/yr and no health problems), but comparison to others and attachment to worldly things.

This is what causes people in the West who earn $35k and $350k alike to feel 'poor' despite the fact that even the former income is already in the global 99th percentile.

[distances]

Yes, but I'd emphasize the "temporary" part: hope of better things in the future is important for the human psyche (for extreme case see religions, for example). Students are full of hope, someone at 24k may feel like they are at a dead end.