One of the reasons I don't usually bow in the main hall is that there are new people doing their first retreat. Sometimes there is a perception in the West on bowing that is not in line with what bowing means and oftentimes in interviews I have to explain it to new people, so that they don't get afraid of it or of the rituals. So one of the reasons we don't bow if there are new people who have never done retreats before, is that we don't want to make the Buddha's teaching inaccessible to them.
We teach bowing to old students because they have had some practice and understand some of the benefits of the practice and are able to have gratitude and respect for the Buddha, the Dhamma, the Sangha. But until people have had some experience of the practice, they can form negative perceptions towards it. Especially the idea of "bowing to idols", this is not what people believe they are supposed to do. So they can misunderstand what it means. That is the main reason we don't bow. When there are only old students, it's easy for us to do it.