Coinbase exchange was launched in 2012 right? Have there ever been any cases of users' assets being frozen and never released to them?
Many of such cases. I'm sure if you count the unreported isolated cases it would reveal a much higher number.
I respect coinbase so much and I am curious why such a thing would happen.
I have no idea why you would respect coinbase. It's an anti privacy company which has been reported to be sharing user details to government authorities, or
selling them in some cases, among so many other ills.
Why they can seize someone's funds is simply because they can. You give them the authority to do that when you sign up and agree to their terms.