1. Your Site does not have a CMS - Most current websites are built using software with standard HTML / CSS based layout. These provide clean source code preferred by Search engines and will help your website perform better for SEO.
2.Your current CMS is too complicated to Use - Complicated CMS will still require technical hand to manage content. Ask yourself if it is easy to add features and content? If not you need a better CMS.
3.Your Developer is too busy - If you don't have an in house web developer then you are forced wait for site updates or look outside the company for help. Wouldn’t it be better if you have a website with simple plug-ins or modules that could be added with very little custom development? This enbales even the very novice to update site using simple WYSIWYG tools.
4.You have Outgrown Your Website - So your company has grown, continues to add new products and services. Your current 10 page website was about how your company got started simple listing of your services. A website that can grow and expand quickly as your company grows will need a good flexible CMS to add and keep current things like FAQs, New services, new information, add shopping cart, request a quote, etc. You don't have to rebuild your website a fresh.