I think this is related to a variety of factors, some of which seem counter-intuitive at first: 1. writing new code is often easier and faster than reading and

I think this is related to a variety of factors, some of which seem counter-intuitive at first: 1. writing new code is often easier and faster than reading and understanding somebody else's code well enough to modify it 2. wildly varying differences in talent and knowledge and skill sets between different programmers and teams. A follow-on guy may be much better, or much worse, or just have a totally different skill set at which he excels 3. old code may "work" and be satisfying a lot of old required behavior but some of that behavior is no longer actually required. a rewrite can get rid of the bathwater while keeping the baby. 4. fashion. the new guys want to redo it OO. the later new guys want to put in more Design Patterns. the later new guys want to add Unit Tests. Then rewrite being totally TDD. Then add Aspects. and so on. Meanwhile.... the core behavior actually needed by the business stays, well, about the same.