Because if total salary income were uniformly distributed across the population, the average would be like $80,000 a year.
And that overlooks that whatever measures would be needed to flatten the income distribution like that would also shrink the overall pie, as in Europe. The fact is that, even accounting for what the OECD calls "transfers in kind" (such as provision of government health insurance) American households have a lot more disposable income than European households: https://data.oecd.org/hha/household-disposable-income.htm (select the "gross, incl. social transfers in kind" drop down under "perspectives").
Americans aren't irrational. The majority is deliberately voting for an economy that produces more disposable income for the top 60%, at the expense of the safety net for the bottom 40%. This feature of the economy is reinforced over time due to immigration. Europeans migrate here to work as programmers, because they can make $500k/year in San Francisco versus $150k/year in Germany. My immigrant mom just came back from a long trip to Australia the other day, complaining how "small and close together the houses were." She said "America is really a land of opportunity. You can get rich here. You can't get rich in Australia." She doesn't care about communities suffering in generational poverty in Appalachia or Baltimore. And she is a party-line Democrat voter!
I don't mean to put words in obblekk's mouth (text box) so what I perceived them as meaning is: I don't think the person you're replying to was advocating for direct person-on-person action. When we see people protesting or pushing back against or loudly saying "this is wrong and I won't have it and neither should you" kinds of things, we should consider how our personal situation could rapidly change to be like theirs. And, in a lot of cases, would have been like theirs but for some skill at leveraging a few strokes of uncontrollable luck.
To me, it's like when people complain that "those damn unionized trash truck drivers are making $90,000 with a lot of overtime and a pension." Why is the response to try to tear them down, when the correct, to my mind, question is "why don't I have that, too?"