This is only speculation but having seen the facility at Ilford as have other respondents, I wonder if there is a chicken and egg situation that may be hindering turn around to an extent. Ilford's problem may be that if it invests too much in terms of experienced staff and/or machines to speed up turnaround, it risks losing money.
Once it can be sure of a certain amount of business on a regular basis, it can afford to invest more. I inferred from what Simon Galley said that the service is there to promote the taking and processing of B&W film and prints and provide a service to trad users and not designed to make money. It will never be a big income stream in relation to Ilford's main business streams. However it hardly makes sense for the service to be a drain on revenue.
If I were a busy B&W photog with little time for the processing and printing, I'd have no hesitation in using it. If I had to describe the service in one word it would be PROFESSIONAL.