Debt fueled by inflationary government money-printing drives wealth inequality between asset owners and salary earners. Newly printed currency boosts asset prices and inflates away salaries.
As Milton Friedman pointed out, it also increases the tax burden on citizens two-fold because inflation causes salary earners to be pushed into higher tax brackets over time as some of their salaries are eventually negotiated upwards to offset inflation.
My guess is that it has something to do with what happened in 1971 when the US dollar (and all currencies which were pegged to it) moved off of the gold standard. This was the time when asset values started inflating. This is why it only affected millennials and they could not afford their own house.
Japan took on more public debt than any other country which is why they felt this effect more strongly since they ended up having to print their national currency at a higher rate (thus resulting in worse asset-inflation) in order to pay off the interest on their debt.