Consider how big the difference is between each segment identified here. Realise that the upper income bracket itself could be broken down into three segments that would show an ever starker difference.

Unequal gains is the problem, and your intuition can help inform why: the 2023 dollar index used is based on what rate of inflation? CPI? RPI? Something else? Why is it that in 1970 a median income household could buy a home on a single income and raise a family (including sending kids to college), on a 2023-dollar income of $66k, but that's mostly not possible on $106k in actual 2023 for most households.

When you adjust for real buying power using a less favourable means of assessing inflation and taking into account housing costs more fully, I sense you'll find that the bottom two brackets are behind their 1970-adjusted counterparts, and the upper income bracket is significantly better off, especially if you then break that upper segment up a little into more categories.

And, without something happening to adjust this, the effect is going to just get worse and worse, and everyone knows it.