Camping is now extremely popular in Japan now. It was popular pre-COVID but getting much popular from 2020. The reason is simple. Campers do not mix up with other people at the camping sites and campers think camping is much safer than staying in urban areas.
There are two types of camping. The first one is overnight at camping site or in the nature. The second type is a spending at the camping site or in the nature during daytime and go back home within the same day. By the way, it is common to overnight at the camping site for multiple nights in Europe but not in Japan.
Actually many people just go for a day trip and therefore they will not bring any sleeping bag to the site. On the other hand, main purpose of their camping is BBQ at the site. Also not only BBQ, many campers cook other meals using frying pans and pots. Therefore main products of camping gear stores are not tents or sleeping bags but for dining - tables, chairs and other utensils.