1. Some companies are so slow and some teams so agile that creating a new working project takes less time than submitting a ticket for permission to install and demo software and get the required permission to purchase it. 2. Developers hate to deal with salespeople, so unless the CICD platform is OpenSource / free the developer might choose to build something simple. 3. Developers might be unaware that a solution exists to solve their specific problem. 4. The commercial solution to a small developer's problem might be too expensive.
The developer estimates of time and money for building something in-house often neglect the "hidden costs" ... (including the long tail). The hidden costs often include : 1. opportunity costs - a developer can't do two things at once, so if they are writing a tool, they are not releasing new features or fixing defects. 2. Maintenance costs - keeping the thing running (when the host OS is upgraded, the network changes, the repository credentials expire, etc) 3. support costs - if this touches any other outside teams or customers, someone will have issues and need support. Maybe a new team has to be created to handle the Zendesk support tickets, provide Slack help, etc.