I'm a user of Bitcoin and I never used any exchange.
Just obtaining Bitcoin is expensive unless you have a high trust off-chain method to prevent double-spending.
Bitcoin is slower than all this and violently fluctuates which loses people's money quickly. People also need to pay their bills in fiat anyway so whoever is receiving the Bitcoin needs to cash out to fiat anyway.
At that point you might as well just use fiat instead.
I did this dance at least 100 times and never ever had a problem with price fluctuation. Bitcoin is pretty stable on a 3-day timeframe.