Both players are aware that the opportunity comes from just being lucky enough to be chosen to dictate the terms. I know you didn't earn the 10,000 so by you offering 100 dollars and you keeping 9,900 is insulting to some people and they do want to punish the 'lucky' player. It's not that they don't value the money they value punishing them to teach them a lesson at $100.

Would your answer be the same if I said I'd keep 9,999,999.99 and gave you only a penny. Would the value of punishing me be so low that now you'd consider to do so, or is it still free money and the absolute value doesn't affect you personally?