Though they did indeed build a RT kitchen set. And later on the set morphed into Julia's office at Windcliff.
Today, what with advanced editing and all, they may been able to shoot in an actual kitchen in the studio. But back then that never would have happened. For one, all the sets were constructed on the first floor and all the offices, dressing rooms, rehearsal hall, etc. were on the second floor - and down on that first floor they had a hard enough problem maneuvering the cameras around the sets for the various shots, much less trying to use a camera up on the second floor.
However, I'm not sure if there even was a kitchen in the studio. Back in '89 part of the Fest activities was a tour of the former studio with DS cameraman Nick Besink and he impressed upon us how the studio had very little in the way of facilities and amenities. The building really is quite small.