Regarding the similarity between MTD mowers and various brands, when you look at entry level machines, they are all going to have the same basic parts. At this level, everyone is going to use a Kohler, B&S, etc engine. Things like spindles, blades, transmissions, wheels and tires, etc are all commodity items and you can mix and match them to make a mower. If I recall, in addition to MTD building mowers, they are a major parts supplier.
There has never been a "Craftsman Mower Factory", they just sub it out to someone with custom specifications. John Deere may have their own assembly plant, but they get most of the same parts everyone else does. If you buy any given part for a Craftsman or John Deere or Husquarvna mower, you will probably find it also fits an MTD and a half dozen other machines.