[EdSharkey]

The psychology of knowing ahead of time you'll delete all the code is interesting. Devs would be in hack-hack-hack mode and not worry about design - the goal is just explore all the territory to find the hilly parts and landmines. Move as quickly as possible and report back.

In general I think developers value their code too much and should be willing to scrap and rewrite, especially whenever requirements are changing. I chalk it up to everyone's desire to conserve mental energies due to not understanding what their energy peak/limits are.