Clubs lose many new members because they were not properly informed about Rotary, The Object of Rotary, and the obligations they take on when they join a Rotary club. Many others are lost because the club either overworked them upon joining or total left them to fend for themselves.
These two links are to documents that, when followed, can help clubs retain new members.
The Membership Process - An easy to understand diagram.
How to Propose a Member (Rotary Form 254)