Well that might of been a good plan when the sim 1st released, but it really didnt happen with the 1st half of the sim, and they have all that old code that still had bugs they needed fix, and then there was the pandemic which who knows how that affected the development at well.
But sure I concur. It would of been the best for everyone if they did a ground up rewrite of the entire game, but we know that didnt happen.