Haha, just kidding. It's actually the opposite. The reason CEOs respond is because they get much fewer emails from customers than you'd imagine. They get their typical solicitations, internal meeting emails, external business discussions, but the customer emails can be interesting and more insightful than any internal letter could be. If you put time into it and write your letter which doesn't require a huge time investment to response (i.e. avoid dozens of specific questions and allow the discussions to be open-ended), you might get a response. If any human is contacted by another of our species, it's intrinsic to want to respond. Being a CEO doesn't remove that desire. Yes, you might be bothering them a bit if they sacrifice family time, but that's their own problem/choice!