> If you develop a program for a long period of time by only adding features but never reorganizing it to reflect your understanding of those features, then eventually that program simply does not contain any understanding and all efforts to work on it take longer and longer.

The author doesn't take the next logical step: what factors prevent the reorganization of a program?

One factor that comes to mind: lack of automated tests. Those working on the program are scared to change anything for fear of breaking something.