I watched the video linked in the article, and I am not sure how they are different from buses? They seem to be completely custom built, making them expensive

I watched the video linked in the article, and I am not sure how they are different from buses? They seem to be completely custom built, making them expensive to maintain or of to build newer larger ones. Edit: I think I realise now that the difference is that you save having to walk up a flight of stairs to the plane, thus you'll never actually be outside. That is neat, but I am not sure it is worth the expense. Other airports have gates where the plane is somewhere else, and it's just buses picking you up, since the buses arrive like regular buses, they don't have to wait for the other one to reverse out. And since they are just buses, getting more buses is easy, and possibly a lot cheaper.