People do not like too many choices and procrastinate making decisions. Even the most opinionated people I know do not always answer your question in a timely fashion.
The easiest way to get a response? Make your question as easy as possible to answer. Don’t bury it with information, encrypt it in an email or forget the question mark. Provide a concise brief upfront and ask a yes or no question. Make it a multiple choice question if you need to. At the very least, provide the recipient with possible answers so he or she does not need to do the research or draft an elaborate answer of his or her own. Take the opportunity to curtail the list of possible answers to meet your own needs. If the recipient comes up with an answer other than the ones provided, whatever. At least you got an answer.
Busy people (like CEOs and celebrities) are notorious for single-line emails. Help them keep that pace and not bog them down with answering your question. The more you help them and consider their time, the easier it will be to get an answer – and the greater chances you will have at getting an answer you like.