Well 7...Bxd6 8.Qxd6 and there are menacing ideas like Nb5 coming up hitting Black's hole on c7. Should Black try to shoo away the queen with 8...Qe7 then 9.Bf4 and I don't see White castling anytime soon, period. (9...e5 10.QxQ and KxQ is forced as NxQ drops the e5 pawn).
Regardless of how solidly black can play on with ...Bxd6, I find it less complicated to do a poor man's castle of Ke7, Re8, Kf8 at some later point.
Needless to say, White locking any piece firmly on d6 is unpleasant for black. Even worse if it is a queen.

Hi,
A friend of mine did an analysis of a game we just finished and in doing so, we were both bewildered by a move made by all masters from a particular position. Here it is:
15 games in the masters database do Ke7. None do Bxd6. Neither of us can figure out why there is such strong consensus for Ke7, which seems to be a weak move and removes the ability to castle later on.Any insight appreciated!