That, and the fact that we don't really revisit the modeling approaches when the constraints that led to them no longer apply. For instance, incremental evolution based on a branch where work was done "by hand" into animals, simpler machines and then very complex machines might lead to a very different result than evolution from a branch where the ability to design some types of complex machines is there "from the start".
Note that this is different than saying "let's completely ignore the past".
Note that this is different than saying "let's completely ignore the past".