Coinbase carries only crime insurance. If they experience data breaches or attack and you lose money because of that, they'll give you a refund but Coinbase doesn't claim how much money they'll refund.
They also don't say how much money they have insured, so, if you lose $1000 because of their mistake, you might receive $1000 or $200 or nothing, no one knows exactly because even if they partner with other insurance companies and are insured, there aren't guarantees that insurance company will cover the losses. There have been many cases when insurance company turned into a scam in the end.
Okay but... what good is that?

They are saying they will "partially" make you whole, but they don't say what "partially" means? So somewhere between 99% and 0.01%? That is the same as no promise at all.
I won't see it as a no promise, there is actually a promise there. Although we don't wish for something like that to happen, but if in the eventuality of things that it does happen, Coinbase saying they will make their customers partially whole, simply mean that, instead of you losing everything, they will give you certain amount to cover your loss. Though it might not be 100% recovered but something closer to that. I think it's a good assurance for Coinbase customers. It is better than those other exchanges that got hacked and their customers got nothing in return as a measure to recover their loss. So if you look at the word technically you will see that there is indeed a promise there.