If that was their goal, they would be doing this to popular civilian rounds. (9mm, .38, .45, etc). Even the .380 is more popular than the .40.
Almost all the law enforcement has now gone to .40 or some to .10 MM. Mostly .40 so I would agree with you that they are buying for some other reason that drying up the supply.
It could be many things and none of it good for you and me.