Just like a Ponzi scheme, they keep piling on. Every paycheck, the 401-k & 403-b portion goes into stocks, 66% of it on average. Who wins in a Ponzi scheme? The initial gamblers. Who gets caught holding the bag? The last gamblers.
Only if they know when it's "game up" and decide to sell. When a selloff happens, it's going to be a huge payday for the gov, because of capital gains taxes.
It is beginning to seem that it will take a crisis beyond the gov's power to manipulate around it to cause a crash.