Coinbase uses ACH (which is reversible) while many other exchanges use wire transfers (which AFAIK are merely more difficult to reverse, not impossible).
Yes, wires are much more difficult to reverse but they can be reversed. In my experience, your financial institution must get your prior approval before reversing a wire (which is not true for ACH reversals). Wires also you a completely different system of clearing funds which is part of the reason reversal requirements are different.