The same reason, a normal person might decline $5 but accept $50 out of a pool of $100. 5% seems more unfair than 50%.

"i have all the money I need" is a different reason to "that's hardly fair!"

It's the combination of the two, I think.

That's hardly fair... but I need the money => Accept.

I don't need the money, but it's fair => Accept.

It's unfair, and I don't need the money => Turn down.