Even if someone says that one shouldn't keep your balances on exchanges, you may see them have some of their stash deposited there for whatever purpose they are doing. Like in interest accounts and earns passively there but they know the risk I guess.
So wherever you're keeping them, you're aware of the risk that you're taking upon keeping it on exchanges. It's not just the newbies that does it and yes also likely the ones that suggests don't keep it there.
Many people also say to stay away from centralized exchanges and only use decentralized exchanges and I don't believe what they say either. I have the feeling that many people are trying to lie to please someone to gain merit rather than telling the truth. It is true that people do not store bitcoins on centralized exchanges because everyone is aware of its risks. But those who say they do not use and do not have any accounts on centralized exchanges are blatantly lying. I bet you that people who say so are also secretly using them because they are almost a necessity in the market and that is why CEX still exists in the market.
For the sake of our Bitcoin's safety, someone probably are keeping all of his assets on a hardware wallet which is the known better storage. And there can be some that keeps only their Bitcoin and yet, most of his alts are left on exchanges for quicker liquidity.
It's okay to use them and you know the risk that you take whenever you leave huge amounts there.