Aside from the regressive tax policies of the last 30+ years, and all those loopholes (carried interest, I am looking at you), the major issue is that we've been in a bond market boom for 30+ years.

Asset prices inversely correlate the with interest rates. Rich folks own assets. Those have increased faster than the growth rate of the economy because interest rates have been trending down for 30+ years.

That being said, we've reached the end of that trade--mostly because interest rates don't have anywhere else to go but up. Overnight rates in most of G-7 are close to 0%.

So if interest rates reverse their course (even if only slightly), the asset owning rich will suffer, and earners will gain.