Pending players are members who have either been invited to join your club and waiting for you to accept them or they have applied through your clublink to join your club . If your club settings are set so that acceptance is done manually by you after you check them out then they will be listed as pending .
Also they may be have been invites by other club members if they have the ability to do so and have not accepted the invitation on their end as well . This too will also place them as pending on that list . I agree with you on how you clear the list once a week or so but you can also check to see if they are in a club which is usually the case .
You can change your club settings so that all who apply can join and then vet them from that end and that should resolve the problem .