You see this same thing happening at law schools as well.
If you look at the faculty of Harvard Law [1], many of the professors have not served in a professional capacity as lawyers.
In fact, many firms have to train their new associates in the actual practice of law because law school itself has become so detached from the reality of being a lawyer. [2]
Part of the problem is that these instiutions are part of universities in the first place. It is only natural that Harvard Law School is going to be influenced by the rest of Harvard. There's even an increasing trend in law schools of hiring people with Phds in other fields as law professors (the attraction for the Phds is the higher pay, lower teaching requirements, and pro forma tenure review).
But what about all the other grads who are doing jobs that are nothing to do with their degrees at all? Entrants into grad training in UK big 4 accounting firms can have a degree in anything, it doesn't have to be relevant. In fact students seem to consciously choose humanities as they seem less daunting than Mathematics or Economics... Makes me wonder why we make people do degrees at all?