Nothing to feel guilty about. The body has its own way of dealing with stress.
I loved my Dad very much! Yet when he died I didn't shed a single tear. It was many years later, something like 10 or 12 years, maybe even more, that I ended up bawling my eyes out over his death. It turns out that my body had shut itself down when my Dad died and I was incapable of feeling much of anything over it. However, years later I went to a funeral for an Uncle (my Dad's brother) whom I hadn't seen since I was a little kid. But he looked so much like my Dad that I just started to cry and couldn't stop. I had to leave the room and I spent the whole service in the ladies room bawling my eyes out ... for my Dad.
Sometimes it just takes time. So don't feel guilty because you don't have any real emotion attached to their death right now. It's your body's way of coping