Simply making out some comparison between custodial and non-custodial wallets which you can eventually tell the difference without much of explanation.
If a certain user could really handle out the risk on using up Coinbase then its up to his choice.The good thing about internal transfers that it is really free of charge
which is already a standard with most platform when making internal transactions but for on outside then its understandable that you would need to pay
up some miners fee. Coinbase doesnt charge out any additional aside from that.
Oh sure, everyone's free to do whatever they like. I mean, isn't freedom one of the main advantages of Bitcoin? The problem is though, that the reason why a lot of people use custodial wallets is because they think that these custodial platforms are "very secure" or "unhackable" or something along those lines. Hence why everyone who knows enough about crypto security is frequently pushing people away from custodial platforms.