The reasons we have against doing it our quite numerous but the main ones are:
- Dynamic map changes are not supported by the engine
- The amount of history work to bridge the gaps
- We have little to no information for pretty much every single house, we would have to make them up
- There are not many historical wars we know off so most scenarios would start off pretty much like the current Bleeding Years bookmark which many have said is boring
- Coding for the andal invasions
- Coding for cultural migrations
- Coding for valyrian succession, they had 40 houses in the freehold who were effectively patricians, ck2 only supports 5 before you get interface glitches and lag if you have lots
- Having many many dragons will almost certainly cause lag and other issues
- 3