It's broken because the interview has little to no correlation of on-the-job success. The current process does a poor job answering: "Can the candidate succeed in the role we need filled?"
One of the reasons I see that happening is because the role itself is so vague that there are no proper boundaries and it is entirely subjective.
Nearly every other industry has things worse. We just like to complain.
Also, we are very quick to jump the bandwagon and not analyse it objectively. The people who say the interview process is broken are themselves selling the same solution just in a different medium.