One of the initial steps taken by any ICO organizer, is to do a market research in order to see what the potential interest would look like. One of the methods often used, is to restrict ICO participation only to "whitelisted" individuals.
In order to get on the whitelist, you need to show interest by filling out a short form or going through some kind of verification. The more regulations will hit the Crypto world, the more in-depth the verification for white-listing will be.