The thing is people use exchanges only for the short trades they make and some people on the forums I'm sure don't store bitcoins on binance or other centralized exchanges but because binance provides a trading service some people still use them today in trading. I've used Binance several times for short trades but it's not for long term use and for day traders maybe some people use a centralized exchange only for trading.

Because it's impossible every day they have to transfer assets to their wallet every time they finish trading, Bitcoin has never followed that centralized exchange which you have to understand and bitcoin has never had anything in common with exchanges as the two are quite different. Who cares if binance is lost or not?