I am also sorry for your loss. 
I think people often don't "know" how to behave or what to say, so they do nothing. It's not malicious or nasty, but they see it as giving you space, or being uncomfortable and not wanting to do the wrong thing.
When I was 17 (a million years ago), my boyfriend's grand-dad (on his dad's side) died of cancer on a Friday night. It wasn't unexpected, but it was sad. My boyfriend's dad always went out with his mates on a Friday night. He umm'd and err'd about whether or not to go out like he always would, and in the end, he went. I was REALLY shocked he went out, because I was brought up in a religion which has rituals around death, and NO WAY would someone 'go out' for a night with their mates unless they were making a statement. (I say again, I was only 17!).
When I told my mum, she said that for CofE people, there's no hard and fast rules like there were for us, and so they don't know what to do in a situation like that. And, actually, my bf's dad prob got a lot of support from his friends, and had an opportunity to let off some steam (i.e. grief) and toast his dad. Plus a bit of normality in an abnormal situation would have been very comforting to him. And a way for his friends to support him too.
So I really, really learned from that, and don't judge what people do around death. It's a horrible time, and leaves those around unsure what to do for the best. NO ONE wants to be the one who gets it wrong, and - often - doing nothing is perceived as being better than putting a foot in it.
When my DD died, we got lots of cards saying things like "I'm praying for you" and people said that to my face too. But my dad was an atheist (despite being born of a religion albeit one that is a minority in this country). He would have HATED being prayed for. So the people who said that, it was more about them than him. But I did recognize that they were reaching out to me/us/him. And that was the important thing, I think.