Coinbase also does not offer any sort of discounts for on chain transactions as well.
Yes, but I think OP is referring to Coinbase <-> Coinbase off-chain transactions which are free.
But either way, while it sounds so attractive @OP (who doesn't like free transactions?), it's downsides heavily outweighs the upsides. Do you know? Coinbase can lock up your money if they want to? On the other hand, with non-custodial wallets such as Mycelium(though I'm personally more of a BlueWallet[1] guy), no one, I mean literally no one can revoke your access to your funds. That's one of the beauties of Bitcoin!
[1]
https://bluewallet.io/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.