Developers generally love the freedom of building greenfield projects. Unencumbered by past decisions and conventions engineers are free to try new things and take blank sheet approach to overall design.
However they come with their own problems and new applications take a lot of time and effort to settle down and become both stable and loved by users. Legacy projects are far more common and often come as a tangle of code with an overall structure that may be obfuscated and where the hundreds of subtle fixes and micro business rules that are coded present and working are not obvious on casual examination.
However with patience and discipline Joe Stead explains how they can be even more rewarding to tame.