I think it makes perfect sense. Those people are building something from scratch. That's a lot more responsibility and skill needed than to maintain a tiny part of a huge well established system. The people capable of doing an A+ job at building something totally new are very few and far between and the competition to hire them is fierce. The best way to move up in this industry is to build up your skill and jump ship to a new job as soon as your skill has outpaced your salary.