A better question might be why did god let a powerful angel known as Satan go to the Garden and tempt those weak human mortals ?
The temptation to disobey God would eventually be insitgated by someone. It doesn't really matter who in my opinion. God allowed it because he loves us and wants to see us live free. It offered him the opportunity to place a certain value on human life by dramatically displaying the price of redemption that he was willing to pay.
How much is something worth? Whatever someone is willing to pay for it. Many people bring objects to Antiques Roadshow thinking that their object only has modest value. When they learn THAT EXPERTS are willing to pay big money for it; it changes EVERYTHING.
Since, we now know what we are worth, we now have context, a benchmark, a scale to see the enormity of what being made in the image of God really means:
For God so loved the world that He gave His only begotten Son, that whoever believes in Him should not perish but have everlasting life. 17 For God did not send His Son into the world to condemn the world, but that the world through Him might be saved.
18 “He who believes in Him is not condemned; but he who does not believe is condemned already, because he has not believed in the name of the only begotten Son of God.