Why are visitors advised not to walk through the center of a torii gate at a Japanese shrine?

According to the traditional etiquette I discussed, people pass through a torii gate on the left or right, leaving the center for the deities. It is a way of showing respect when entering a sacred place. Similarly, some temples reserve their central entrance for the deities, reminding visitors to be mindful of how they enter and leave.

From a religious perspective, a torii marks the sacred boundary of a shrine. Passing through it means entering the domain of the deities. It is therefore more than an attractive entrance or a place to take photographs; it is an entrance to a place with religious significance.

We once discussed a shrine we had seen in Nara, where the central passage was closed off and opened only when the portable shrine passed through. At the time, we also mentioned that some Japanese people now walk straight through the center. We should not assume that everyone follows the same practice simply because they are Japanese. What I wanted to explain was the respect for the deities and the place behind this traditional etiquette.