Question: Why not take over this planet's cloning process instead of shutting it down and recruiting others to be Stormtroopers, when the clones were 100% obedient and loyal to the Emperor?
Answer: There would be serious moral and ethical issues about cloning sentient beings just to become mindless, obedient servants/slaves/killers to achieve your cause, regardless of its good intent.
But the Empire clearly doesn't really have moral/ethical issues about most stuff, so that's not really an argument.
Ray West mentions "mindless, obedient" servants, which is a good point. I think an army of "mindless" clones would actually be less effective. Instead, the Emperor claims that the Jedi wanted to overthrow the Senate. If he can persuade a decent number of people to support him, and spread his way of thinking, he can slowly gain more influence around the galaxy.
Answer: I think recruiting people is one of the sneaky ways of controlling the galaxy. Many Stormtroopers might have spouses and children back home. They could be receiving a tiny salary. Maybe some younger adults are eager to get away from their home planets, as Luke and Anakin both were. Still, others could be criminals who agreed to serve as Stormtroopers instead of another sentence (in "Game of Thrones", some convicted criminals can choose to join the Night's Watch order). These would all be ways to convince more citizens to support the Empire, instead of just training clones.
Azalea
I'd like to add besides these points that it's possible the cloning process is just too slow and cumbersome for the Emperor. They were useful as shock troops, to fight droid armies. But their numbers were not great enough to cover the entire galaxy as a security force. This especially once the Rebel Alliance shows up. I'd say recruiting people gives him a much-needed manpower boost in a shorter time.
lionhead
Time-consuming, cumbersome, and not a great number produced as you pointed out, as well a a massive expense.
raywest ★