Continuity mistake: When Homer and Bart are on the motorcycle trying to get rid of the bomb, the bomb slips out of Bart's grip. When he's hanging onto his father's shirt, Bart first grips the bomb's handle with his palm and fingers facing the front of the bomb, with the clock. Then when he's hanging onto his father's hair, Bart's hand has flipped around and he's now gripping the bomb's handle with his palm and fingers facing the back of the bomb. Something to look out for is the shot just before the close-up of Chief Wiggum, because as Bart raises his arm the bomb actually flips over in his hand while we're watching. Quite impossible. (01:12:55)
Answer: Homer has been known not to make the smartest decisions, and the decisions he does make, he makes without fully thinking them through. Clearly he wanted to get some donuts as quickly as possible without thinking of any other ways, so he decided to ditch the silo in the lake as it would be the fastest way of getting it off his back, even if it's not the smartest. Also, putting that aside, he likely wanted his own pick of the donuts rather than have Lenny guess what he wanted.
Casual Person