The motivation for doing experiments in economic and management science is much the same as in the natural sciences. The laboratory environment is controlled and can be made relatively simple, conditions that are conducive to exploring new ideas and concepts.
The physicist Richard Feynman explained the role of laboratory experiments with an analogy that is particularly apt here:
If you play chess you must know that it is easy to learn all the rules, and yet it is often very hard to select the best move or to understand why a player moves as he does. So it is in nature, only much more so; but we may be able at least to find all the rules. ...How can we tell whether the rules which we "guess" at are really right if we cannot analyze the game very well?...First, there may be situations where nature has arranged, or we arrange nature, to be simple and to have so few parts that we can predict exactly what will happen, and thus we can check how our rules work.
The difference is that, in economic and management science experiments, we simplify the rules of the game to better understand why a player moves as he does.