Lowes and Home Depot are publicly traded companies and need to keep their stock holders happy by maximizing profits. I doubt they would ever go heavily into any hobby, especially one getting smaller like O gauge trains.
As railbear601 mentioned, Menards is a privately owned business mostly owned by Mr. Menard. He can do pretty much what he wants, and since he enjoys O gauge trains he has his stores sell them. Nice to be The Boss. It will be interesting to see what his family does with the train line when he passes.
