[tristanj]

As long as the money supply keeps increasing, excess money has few places to go (bank deposits, stocks, real estate, and physical goods). Most of it will go into the stock market, since it's quite liquid with and has good investment returns.

Also, a significant part of the stock market is driven by foreign investment. The US has few capital controls and is an easy market for foreigners to invest in. Around 1/3rd of US stocks are owned by foreigners.

Even if the older generation sells during retirement, foreign investment will be more than enough to replace it.