Home prices relative to incomes were low in the 1980s and the 1990s. Home prices boomed in the 2000s while incomes remained flat. Homes were cheap in the wake of the 2008 housing crash, but unemployment also went to double digits which made it hard for established millennials to buy homes. Home prices have essentially recovered now, and while jobs are easy to come by in 2018, wages are still low.
Homes in metropolitan areas with tens of millions of immigrations have rising prices, but rural America is very affordable.
Millennials also do not start working at 16 or 18 like most of their parents did, so they delay their income too much into the later parts of life.