Why would people give up the opportunity to cash out the winnings of investments/gambles? People do the same with some stocks.
If you believe that Bitcoin has a bright future and even may become a global currency, it's a bad investment move to sell your bitcoins at any time. Sure, you can argue that you can sell high and later buy more for less but that's timing the market and no one can actually reliably do that and as a result if someone believes that BTC will be huge in the future will never sell. When the mission is accomplished, they will use it as money to purchase goods and services.
Here's a thought, if your medium of exchange is someone else's cash-out, pump-and-dump opportunity, then maybe it's not a good medium of exchange.
JP Morgan spoofed the precious metals market and got caught.
In the medium of exchange category, the forex market has been manipulated for decades.
You are more at risk of volatility and manipulation in crypto markets because they are immature. Bitcoin is still in the discovery stage.
Well yeah, that was my point. That's why in many countries with rampant inflation they use USD or EUR, as mediums of exchange because they're currencies controlled by powerful economies and governments which have proven to be mostly stable throughout recent history, save for major disasters, therefore their currencies exert a large amount of trust and stability on the financial markets, vs BTC that fluctuates more extremely more quickly without any brakes from any government as the BTC you got yesterday for selling your PS4 on ebay could maybe now buy you a yacht or maybe not even a big mac.
Also don't forget that if it happens that BTC replaces the government controlled currencies as some pundits claim, there won't be pump and dumps etc. No one pumps and dumps USD in the USA but they do it in other countries.
A quick example is Turkey where the USD gained against the Turkish lira a lot and lost over %30 value overnight but USD is still good.
Your comment serves to make a point for strong and stable fiat like USD, not for Bitcoin which also just lost around 40% of its value in a month.
BTW I don't hold any crypto, I simply find it fascinating and I think there's some merit in its ideas and technologies.