You are due capital gains taxes on any gains resulting from the sale of bitcoin regardless of where the coins are held
If ones Bitcoins purchased through an onramp are immediately spent, or lost , or given away, than their are no capital gains to be paid.
Storing BTC in the coinbase vault will expose you to capital gains in the future.
If the coins are lost then you can likely consider them to be "sold" at zero and would be able to claim capital losses. If they are spent at the exact same price they were purchased at then you are correct, no capital gains are necessary as the coins would be sold at the same price as they were purchased