CAD flow may start out as simple shell scripts or makefiles that you can create in hours or days.  But as your needs grow, such as
Adding new tools Adding new methodologies (design explorations, verification regression, functional safety, design for test, design for yield, etc.) Adding new infrastructure (Compute farm (LSF), Cloud, emulators, prototyping board, etc.) Adding more users Adding more features/capabilities (license optimization, disk space optimization, etc.) …
Those few lines of shell scripts of simple makefiles will start to look like a software project.  For example, a verification regression flow for a successful semiconductor company can consist of 10,000+ lines of python/Perl code.  Owning such software would require teams of engineers, regular bug/enhancement support, training, etc.