I think this misses the point which is Why does Nick Wilson want to legalize it? It is important to note that most of states you have listed appear to have incest laws that are based on very old statutes and seem to have gone mostly unchanged over the years. The point of criticism towards Nick Wilson is that Kentucky currently actually has an incest law that matches modern societal expectations yet he wants to change it. (To be clear, I think those states that currently have it legalized should reexamine their incest code.)

California seems to have defined incest in 1872 when first cousin marriage was seen as more acceptable (still very gross imo): Link

Vermont seems to have defined in in 1797. Link

Massachusetts codified it 1648. Link

Colorado looks to be a bit more recent, as it looks like their incest laws were at the center of a court case in 1966 but that case does not involve a first cousin, but rather a step daughter (the whole case is still disgusting.) I am finding it more difficult to find official documentation as to when their laws regarding incest were first codified, however, I would assume it would be around 1875 when Colorado officially became a state.

Regardless though, it would seem that even when updates are issued to the criminal code the provisions pertaining to incest laws are laws rarely updated.

This, of course, begs the original question of Why Nick Wilson wants to update this in the first place, especially when first cousin marriage is now frowned upon and can lead to generational, genetic abnormalities? Old laws are typically modified to better match the society they govern.

Edit: Nick Wilson now claims this was filed in error, so I suppose that answers the question. See the new thread.