People can and do vote for things that give no benefits to them if it aligns with their concept of fairness. In this case, if you believe a person deserves to keep as much of their income as possible, you will vote for lower taxes, because it feels right.
https://www.nytimes.com/2014/04/20/opinion/sunday/from-rags-...
TL;DR:
> It turns out that 12% of the population will find themselves in the top 1% of the income distribution for at least one year. What’s more, 39% of Americans will spend a year in the top 5% of the income distribution, 56% will find themselves in the top 10%, and a whopping 73% will spend a year in the top 20% of the income distribution.
The reverse side of that phenomenon applies, as well - a significant portion of the population will find themselves in the _bottom_ part of the distribution at some point in their lifetimes, as well.