This is pure speculation, but I wonder if it might also have something to do with surplus cavity magnetrons (and the production facilities for them) becoming av

This is pure speculation, but I wonder if it might also have something to do with surplus cavity magnetrons (and the production facilities for them) becoming available post-WWII. I can't find anything definitive on production models, but I was able to determine that the prototype magnetron that Churchill sent to the United States in secret operated at around 3 GHz...pretty close. Maybe cheaper to use the ones that already had production lines set up, if they were otherwise workable?