You had an awesome site created for you, but your relationship with the development agency who created it ended and now you don't have anyone to maintain your site.
Your site has aged and is accumulating small bugs and issues that your customers are complaining about. You don't know how to fix them but they are only small issues and your site continues to function.
Your site looks good and is running well but you want some small new features added. You don't have an in-house developer, it is too expensive to get a large company to do a small job and it is too hard to find a freelancer.
You have an in-house team or you are a development agency, but maintenance of older sites is taking time away from developing new ones and you'd rather focus on building new sites.