A few years back we developed a website for a fairly large business, they require a full CMS which would allow them to manage their marketing banner, manage a Google Map of stockists and manage all their content pages with ease.
A few years later as WordPress became more developed, we realised that we had basically built a system that was so similar to WordPress but didn’t have the global development that WP now had, so the next version of their site we moved it over to the WordPress platform, this time they got more for their budget!
That said sometimes an in-house CMS is require for certain situations.