Building and maintaining your own CMS involves a significant amount of time and money. This is a task for highly qualified programmers and developers. Costs are high, system development is slower and security is low due to lack of sufficient time/money for security analysis and verification, as well as a small base of users to test the system.
Own content management systems are often developed by large web agencies, which use them to develop a large number of sites - only then the cost of creating and maintaining the system is justified.
However, for customers - users whose sites are built with the developer's own CMS, there is one danger that should not be overlooked.
If you are not satisfied with the work of the developer or there is a problem with the work of the service provider (for example, unexpected rise in maintenance prices, change of management or even closure of the company), it will be extremely difficult or even impossible to find someone else to continue working on your website. Because others will not know the details of operation and maintenance of a unfamiliar content management system and will not be confident in its security.
You will have to hire another agency where the website in almost all cases will have to be redesigned. This can cause you to lose a lot of money invested in the website, as well as lost of significant content for your website created over the years.
Therefore, in our opinion, it is advisable for small and medium-sized businesses not to use content management systems that are privately developed and owned by a separate web agency, but public CMS - paid or free open source, which are used by many thousands of web agencies.
Such content management systems have good and comprehensive public available documentation, numerous communities from which an answer to a question can be sought and secure permanent maintenance now and in the future.
This guarantees that if you decide to change the company that maintains your site, you will not have to rebuild the website again from the start.