I've kept some of my coins on Binance for like three years and I haven't lost any. However, I knew what I was getting myself into by doing so, they could've locked my account for any reason and could've ended up losing my assets. I think some of us are addicted to convenience even we know the risk. Those who stick to " not your keys not your coins " rule are usually people who've had a bad experience and have lost a lot of money by trusting a third party.
We like being convenient and that gives us confidence that our funds are safe in an exchange like Binance. But we all know that there should be some thoughts from us despite having that trust and confidence from them. If we have no intention of trading there for so long, it's better to keep the funds into a hardware wallet.
Binance is a good and reliable exchange but will still need to be very careful not to put out coins in an exchange that could be hacked or our account ending up being hacked. Yes, Binance was once hacked but the team was able to refund customers money because I think they were very reliable.
Not your key not your fund is the advise to every investors that has coin on an exchange to be very careful the way they leave their funds on exchanges because anything that happens to the exchange will affect customers too.