Sure, but stock market investing is no different. Once you’ve saved “enough”, you need a place to store wealth that isn’t cash. If you cash out on a winning stock, that money is likely going into other stocks, or real estate, or some other financial vehicle.
As an aside, all the punditry around a former billionaire president who can’t raise 450M in 30 days are playing on the fact that many people do not realize this. No billionaire has a significant fraction of their wealth in cash unless it benefits a short term strategy or they are rebalancing. Those with money put their money to work through investment. Net worth is based on the estimate of those holdings.