Most non-profit associations don't have full-time personnel who can maintain a web site. Usually a member volunteer takes on the responsibility of updating memberships, current events and issues on the web site and this can take considerable time and knowledge. The alternative is no web site at all - or the services of an expensive professional hosting service on a continuing basis.
As an active member of our local merchants' association, I created the infrastructure for our website a few years ago. We are an all volunteer group with limited time and funds to maintain the site. The model I designed has worked so well for our group, it was suggested I offer it to other, similar organization.
The most time consuming (and expensive) part of building this type of web site product is complete. The user interface is re-usable by any organization without modification. The underlying programming and coding (PHP and MySQL database integration) requires only minor modification for each customer's needs. This helps minimize set-up costs and limits recurring costs to as little as $20 a month.