For short term investors, they want to cash out once the btc hits her all time high and then invest their money on business waiting gently for the fall of bitcoins when they will start buying again. So with cex, it is easier for them to sell from btc to fiat since they are short term investors who are ready to leave the scene.

Another reason is lack of proper education. When I started, I never knew the difference between DEX AND CEX, so I could use was CEX. But discouraging thing then was that the one I was using charge so high. There was a day a made profit as a new investor and I move my coins to another exchange thinking miracle will further happen there, 😂 but unfortunately the reverse was the case and when i tried to move my coins out, my former profit and my money now became the fee. It was a painful experience for a new investor like me as at then, after that I stopped using the exchange which I don't think the exchange even exist anymore.  So one reason to use exchange at times is due to lack of proper knowledge.