Because most really good designers also did low level implementation? Thompson, Ritchie, Leroy, Torvalds. Heck, while I don't know for sure, probably Dave Cutle

Because most really good designers also did low level implementation? Thompson, Ritchie, Leroy, Torvalds. Heck, while I don't know for sure, probably Dave Cutler did, too. I don't know any product that's pleasant to use that was developed in the way you describe. Python certainly wasn't.