Why can't they learn?

Why can't they learn not appropriate behaviors and appropriate ones? I am SO tired of putting these kids in time out and taking privileges away over the same things day after day after day. I am SO tired of the temper tantrums and hearing "You don't like me." when I have to get after them. Josiah is really getting an explosive temper. He doesn't take NO for an answer. I gave them a cup of cereal this morning for part of their breakfast. After 45 minutes, I told Josiah that he had 5 minutes left to finish up his cereal. He continued to dink around and when the timer went off and he knew I was going to take his food away, he started screaming and kicking and flung his food all off his tray and onto the kitchen floor. I told him he was now going to clean up his mess that he made which totally put him into a rage. He was kicking, screaming, and flailing all over the place and flinging the food all over the place even more. I told him he could choose to stop his fit and pick up his cereal or he could keep making an even bigger mess because of his fit and it would become harder to clean up. He chose to keep throwing a fit. 25 minutes later he finally calmed down enough and the cereal was finally picked up. We talked about why that happened and how he needs to start making good choices and learn to control his temper. No sooner is he out of time out, he goes into the playroom and snatches something from Baby T. I told him to give it back and he flings at her, slams into the window, and tries to kick me all while he's screaming and crying because he can't have the toy. I put him back in time out until he can calm down. He continues to scream and cry and I tell him that the timer isn't being set until he calms down. He finally calms down and does his time out. Now he's screeching and crying because I won't let him play with the cords on the vacuum cleaner. I'm keeping a behavior log so I can give it to the behavioral therapists that work with our family as I want them to see the consistency of everything...all the time outs and the repeat behaviors. I just don't know how to fix it all anymore. I don't understand why they just can't learn...things would all go so much more smoothly if they could learn. They are all good kids when they want to be. I try to give them as much attention and do fun stuff with them and I praise them up and down when they do good. I hate it that I have to stay on them like this and that a 5-minute chore turns into something taking me 3 times as long because I have to stay on top of them and get them out of things. They no they're not supposed to be upstairs without permission, that they don't go into Deidra's room, that they are to stay out of our room, that they aren't to touch the computer without having to permission to use it and without having one of us next to them, they know they're supposed to stay out of the pantry and the refrigerator and that they're not to touch the tv, DVD player, and the DVDs. Yet, every 5 minutes they're doing something or they're having issues playing. Why can't they learn? I hate having to keep saying the same thing over and over, I try to keep them occupied playing, learning, doing games together, therapy, getting to do fun things, and they earn their rewards strips and gummy bears for good behavior. I thought all that would be enough of an incentive...in the meantime I keep plugging along, we keep doing therapy, we keep talking to counselors and therapists, and we try to come up with new strategies to try. I just don't understand...I love them with all of my heart, they are all given plenty of love and affection and praise. Yet, it's the same things we deal with over and over and over.... Abba, give me your patience and your love and compassion and fill me with your Spirit today. Help me deal with all these tempers and help them to have more obedient hearts. I know they're going to get it eventually...I'll keep plugging along. I just get frustrated sometimes.