Why does nobody in Jonas' world seem to question the way that things work?
This is a good question to ask. It seems hard to believe that people would simply go along with all the rules, with people being put to death, with the complete lack of choice. However, there are a few aspects of this dystopia that are important to bear in mind. The people have no memory of anything before their own lives. They have no knowledge of other ways to live. The people have the necessities of food, clothing, shelter, and safety, and the people take some sort of drug that represses their emotions, at the very least, their libidos.
Imagine that you live in a community in which all choices are made for you. You have no knowledge of any time past in which people made their own choices because memories are not handed down from one generation to the next, and there are no books, newspapers, or magazines that would reveal what life used to be like or what life might be like in other places. It is a human tendency to believe that the way things are is the only way they can be, and if we have no knowledge to the contrary, we tend to accept the status quo.
Imagine also that you have a perfectly good roof over your head, food in your belly, clothes on your back, and a safe and pain-free environment. Giving all of that up would not be so easy to do. Imagine that you would need to make your own choices, on marrying or not marrying, having children or not having children, what kind of work to do. That sounds like most of us, but you would have had absolutely no practice in making decisions, not having been brought up to need to do so. In the real world, most of us bring up our children to help them learn how to do this, for example, letting them choose between two shirts to wear to school. In this dystopia, even children's hair ribbons and jackets are chosen. As they grow older, their entire lives are set up by the Elders. No one in this community is equipped to make choices.
It appears that emotions are almost completely suppressed in the story. Love does not exist, sexual yearning is suppressed through drugs, and anger is actively discouraged. The implication of this is that people will conform because they do not have the emotional wherewithal to protest or rebel. We are motivated by our emotions, whether they be love, anger, jealousy, envy, or happiness. These make up the human drive.
All of these, the lack of memory and knowledge, the safety and security, and the deliberate suppression of emotion, in combination, create a world in which people will do what they are told. Only the Giver and Jonah understand that this is not a world that is good for people, that human beings need to remember, to know, to feel, and to make choices. Even if the choices are not good ones, this is how we are meant to best live.