It is an absolutely normal thing when the number of constantly active users of a service or website is much less than the total number of registered users. In the case of freebitcoin, they have several hundred thousand users who are active on a weekly basis, and it looks like a great result to me. Of course, there could be millions of "dead" accounts out of 52 million accounts, and freebitcoin could delete them as some other services do. However, I don't think it makes much sense.