Why are games colours generally flawed/weak

I've been wondering lately why it is in most, if not all cases games benefit from reshade. Is what reshade does completely doable within game engines or is there a performance hit for doing what it does even within the game engine that's deemed not worth it by the devs?

Attila total war and to an even larger extent Fallout 4 comes to mind for me. Fallout is probably the most demanding game I've ran on my reasonably high end machine and it does have some technical stuff going on like volumetric lighting, but its also one of the worst looking games I've played in recent memory with the least impressive visuals because the colors are all completely off. The thing is, with reshade the performance hit of the demanding technical stuff seems justified, but it just seems like a waste without it. Most games I've played look better than a vanilla fallout 4 without all that just because the colors and lighting are well done.

I'm aware that I'm probably going to get a reply saying its completely subjective but there's a difference between style and plain bad taste.

One thing is that all monitors display colors differently. What may have looked great on the studios screens (which are usually color corrected), could look awful on my local PC monitor (which is not).

Makes you wonder about the games that do have really good colors and don't require our tinkering.