I already posted a thread about this.
After RTW it is annoying to find the option removed.

Did someone say historical reasons?

If it was historical I would be less annoyed but I find it far less historical to see true offspring overlooked as the honour is bestowed on an in-law. That means my glorious ruling family willingly gave away that rule which is of course absolute nonsense.
I never thought I'd praise RTW but the family tree was better in that game, I thought we'd get extra in M2TW

..........Orda