Of course, from my study of human nature I can see why he would not tell us when. See, if you don't agree. If we knew when Jesus was coming back, one group of people would get ready immediately and then relax or wait for the time to come. They were trained by parents like me who tell their children, "Get your work done first." After the children's work is done, then they can play and do whatever. So also, these Christians would rush to get done all that they think Jesus would want them to do, and then stop, relax, and wait until Jesus would return. What would they do between completing their work and and Jesus coming? I don't know. Maybe, nothing really sinful, but they definitely would not be focused on Jesus coming back. They would be just "hanging out." Maybe, they would entertain themselves through TV, movies, or the Internet. Maybe, they would sleep more or go out to eat more often. Maybe, they would find odd jobs to fill their time. Some people might call this "retirement." Either way, these people would lose their focus on the coming of Jesus.
Another type of people would put off until the last moment getting ready for Jesus to come. And naturally, they would be late. They would find other things to do first (things the above people would do after they finished their "work" in retirement). And then, if they remembered, they would rush to do all that needed to be done right at the end. That's how they handled their big assignments in school. The teacher would tell them they have a large project to do, maybe a 10 page paper, and it was due on April 30. Well, they would begin the project on the evening of April 29. If God told us the exact day and hour Jesus was coming, they would not begin getting ready until the day or the hour ahead of time, and by then it would be too late. Why would this happen? Because they would not have their focus on Jesus soon enough.
So, God in all his wisdom, doesn't tell us when Jesus will come. Not knowing is supposed to help us maintain our focus on him. If he told us the day and the hour, it would hurt us more than help us. We just couldn't handle it.
Peace be with you!