I would think that the jack stand would be less wobbly than the scissor jack if there is a side to side load applied.
It would be difficult to locate the jack stand directly under the trailer frame, and level the trailer, without using a floor jack or something. Perhaps another reason is to lower the overall height of the RV, so there is one less step to get into the RV.
Removing the tires prevents trailer theft, and in a site where the owner might only show up once every 60 - 90 days, it would increase security, and also not 'rot' the tires on the trailer, as they can be used on another trailer that is being moved more frequently, and a newer set installed should this trailer need to ever be moved - say in case of floodwaters coming closer.
Fred.