I think the biggest element in the cost, aside from fashionable profit margin of course - is compliance with health and safety standards, as well as (First world) labor cost. The latter which requires skilled laborers to receive insurance certification.
When selfbuilding, and without needing the trailer frame, I’ve seen kits at around 1/4 of the price. Of course, they have no designed finish yet and tend to be minimum option for everything. What I like most about this one is that they offer leasing at similar price to living in a care home (since food not included in wheel pad lease).