We get a lot of suggestions every day, but there is much, much more to editing than just reviewing suggestions.
Many categories get so many garbage suggestions that it is not worth the time and effort of wading through them.
Many categories rarely get suggesitons -- but are worth developing.
A lot of time is spent developing and refining the taxonomy -- technologies and industries change, stuff happens locally and internationally, etc.
We also work hard to try and maintain the quality of existing links (we even have a forum thread dedicated to just that purpose). Link rot is a reality, so are hijacked sites, and sites where the content has radically changed. I also think that about 10% of all real estate agents change agencies each day.
Other editors help develop tools so that those of us who are programming challenged can be more effective during our volunteer time.
Plus, there are days and weeks (sometimes months and occasionally years) when one just does not feel like editing -- so one does not edit.
Still, we continue to grow the directory - which is our overall goal.