they all have more important things to do than play tour guides to people who aren't even pupils there yet but what would be the point of giving tours to people who are already pupils?
I wouldn't expect the head to give a tour. I would prefer it if I was given an opportunity to at least meet the head and a couple of teachers to get a feel for what they are like.
My DC interviewed at a middle school. We weren't expecting a tour at that time, but when the teachers interviewing them found out we hadn't been on a tour already, they asked the head to take us around and she did, on the spur of the moment. She took us into several classrooms during lessons and introduced us to many of the staff. I certainly gave us and the DC a good feel for the place. Even though the building was older and a lot less well funded than the local school, the DC have had a very good three years there.
At a high school we booked in for a tour. Nobody greeted us or knew why we were there or where we were supposed to do. This was an enormous 3,000 pupil high school so that was a problem. We found the place and the teachers doing the presentation were late, as was the head. The head grunted at us and that was it. The teachers took us on a tour of the most depressing place I've ever been, which includes chemical plants in Grimbsy in the depths of Winter. I felt like the staff were well meaning but not backed up.
At another high school the group booked on the tour were greeted in the office, were taken around by the head and a member of staff, we saw classes in action and met several teachers.
It later turned out that the schools where the head is interested enough to give a tour had mostly well behaved pupils, glad to be there, and enjoying the experience. Possibly because the heads are good at choosing who attends and are interested enough to weed out the ones they don't want. The school with the lackadaisical head has classrooms where pupils have to wear headphones to deal with the noise, where teachers can't teach as they are doing classroom control the whole time, a lot of students are very unhappy there.
I understand heads can't be available for tours, but it would give me a better feeling if they do what schools in my area do - set specific times available for tours so they can meet prospective parents.