I am so sorry for your loss.
But the reality is that everyone greives differently, and so there is never really a right thing to say. Because what for one is insensitive may help another to try to regain normality and vice versa. And tbh even "I'm so sorry" is just a clichet. People say it because it's expected, and yes, because they don't know what else to say.
One of the school mums' dad is currently dying of terminal cancer. She is already grieving for the loss she knows will happen in the next few weeks, but she doesn't want to talk about him, doesn't even want people to ask how she is, she would far rather people just didn't talk to her at all.
Similarly my BIL's brother died very suddenly a few weeks ago. And the reality is that there is nothing you can say to make that better. The day he died I didn't want to call as they were all at the hospital, but I didn't want to not acknowledge his death. So I sent my sister a text, and when I'd sent it that just seemed so impersonal, but had I not sent the text then it would have seemed as if I didn't care... there is no right or wrong way tbh.
I spoke to my sister the next day, but didn't see BIL, and his mum, for over a week. And at that point they wanted to talk about normal, every day things. So what do you do? Take them to one side and bring up their loss and potentially bring them back down?
Your anger is understandable, but it really isn't black and white.