Inequality is still important even if everybody is getting richer (I disagree that everybody is getting richer, but that's a different discussion). Because wealth and power concentrated in the hand of a few means that a few have outsized influence on politics and society, which is very much eroding the fundaments of how a democracy is supposed to work.

Furthermore, there are many studies showing that more wealth inequality results in more consumption in a society. Which is not good for many reasons.