One possibility is that your barber may not be as confident in doing shaves as he is doing haircuts.

I've heard of some barbers warning people off rather than risk cutting them if their equipment or technique is not up to scratch. The last straight razor shave I had at a barbers was not very close, I asked why and they barber said they preferred to err on the side of caution and not risk nicking the skin or causing razor burn. They also told me I'd probably be able to shave myself closer as I know the contours of my face better, since I shave myself every day, and they don't.