Modelers stopped buying them so they were dropped. No sales means no availability. Kit sales have tanked in the past several years. The ones that remain are just barely making it, with one or two exceptions.
I can understand that looking from the viewpoint of the cost of manufacturing and stocking a particular kit. That said judging from the turnover of Balsa, Ply, Liteply, Bass, and other building materials at my LHS, I would say building is starting to grow again however; that is not necessarily an indication of new kit sales. A lot of guys now days are building from plans and going to laser cutters to cut shaped parts to get exactly what they want in a project.