Why is there no bird's nest at home?

Swallows like to nest under beams or rafters. After choosing a place, the male swallow helps the female swallow the mud. They fly to the place where there is water, fill up the mud with their beaks, bring it back one by one, to the point where they can pick it up and pile it up into a dish-shaped nest. Swallows nest from bottom to top. Swallows bring mud balls the size of soybeans to the bottom every day. Each floor moves outward and gradually becomes larger in area. Each small clay ball is uniform in size, staggered and stacked layer by layer, and looks neat. It is glued with saliva, and the mud is United and strong, and it can't be broken without external force. The swallow nest is very small below, growing up and approaching the roof. Swallows will leave a gap. At this gap, swallows will continue to build a platform with mud, like our balcony and our porch. Bird's nest hangs on the roof like a cut durian, and the entrance and exit are egg-sized. It should be no problem to squeeze five or six swallows in such a nest. Every time I look up when I go upstairs and downstairs, there are new changes in my nest. The top one or two rows of mud balls are wet, just like the new bricks laid by bricklayers when they build houses, all of which are soaked in water. A week passed and a new nest appeared at the corner of the stairs. Strangely, after the new nest was built, no swallows were seen living in it. Is it necessary to decorate? Of course not. After thinking about it, I think the new nest is not completely dry and the strength has not reached the requirements of swallows. Just like concrete has a curing period, bird's nest has to be dried for a period of time before it can be moved in.