In recent 1st Match between Maguns & Karjakin, started with Trompowsky. How can Karjakin prefer catsle even g file is open ( g × f6 at 3rd move ). Whats idea behind it?
A few thoughts:
Leaving the king in the centre or long castle are not attractive either with all the open lines and pinned knight on c6
The g file is open but it is not easy for white to make use of it. White has exchanged its bishop which would have had a good square on h6. Also black's pawns on e6 and f6 cover important squares that could be occupied by white knights.
The centre is open and if white concentrates forces on the king side, black will very quickly push through on the queen side and in the centre.
It is an opening and has been analysed by humans and computers and found to be OK.
Also with a queens side castle it would take the king two extra moves to get complete safety for the king and that would make black lose tempo and might lose the game especially when it's against carlsen.