Why does anyone need to cash out their bitcoins? Bitcoins can be used as currency, so why does anyone need to convert back to dollars? If everyone just stopped doing that, we would eventually end up with a bitcoin-only economy.
Because if nobody did that there would be no way for people to acquire Bitcoins and then whole thing would collapse. Are you really that dumb?
If anyone is dumb, it's you.
Where do your dollars come from? Do you buy them with bitcoins? Or do you get them, because you sell something to others? (e.g. workforce)