Exactly this. I view rewriting a code base, even if I am copy and pasting some things from the existing one a way of either learning or refreshing my knowledge

Exactly this. I view rewriting a code base, even if I am copy and pasting some things from the existing one a way of either learning or refreshing my knowledge on how the system works. An added kicker, I have actually gone down this road, and later realized the only thing I needed to do was make a small change to the existing system, so I did just that and discarded the new work. Business got their new features, delivered on time, the system was still stable and reliable, everyone was happy, and now my domain knowledge has increased significantly so that new features and development or bug fixes will be even faster.