Most of them make more money abroad than they do in the U.S. Setting up foreign branches is critical for their ability to reach new markets. Most of these branches are setup by U.S. citizens or permanent residents who have a deep history with their U.S-based employer and often personal connections with the executives at the home office. It is much easier to retain and pay these people if the bureaucratic hoops for retaining American citizenship abroad are less, and they will be less tempted to jump ship and set up competing businesses that jumpstart a foreign country's industry if it's convenient for them to stay American citizens.