Uchiha Sasuke has never stopped to grieve for his family. If anyone would have asked him why, and had he been in any way and/or form inclined to answer, he would have simply told them that he could never really find the time; he's been far too busy training, which is more important, anyway.
So it didn't quite make sense to find him standing in the rain, his sandals slowly sinking into the mud as he looks outwards at an orderly row of graves, each one of them containing (whatever he left of) the remains of one of his family members. It doesn't make sense that he has memorized the location of every single one of his clanmembers' graves, that his eyes can immediately find (third row down, eleven across) the location of his father's grave as his clenched fists turn sheet-white.
If asked, he would have shrugged and said it was too wet outside to train.
Of course, he'd be lying.
Uchiha Sasuke has never stopped to grieve because he knows that if he does, he'll never be able to stop. He knows that, and that's the reason he never allows his tears to stream down his cheeks (avengers don't cry) and mix with the rainwater, why he's never told that row of colorless graves anything but promises to kill (because what's the use of living if he can never push his own hand through the broken remains of his heart?).
Uchiha Sasuke is an avenger, and avengers know better than anyone else that it is easier to kill than to grieve.