What you're describing is people experiencing grief. I'm what you would call an "extreme doomer", and did feel this way about a decade ago when I first realized the dire situation we are in.
But your first reaction is not the end. Waking up and accepting our state, and the despair that came with it, was the first stage in a long process of learning to live, and be comfortable in the world the way it is.
What you are suggesting is that we just ignore grief and pretend nothing is happening. I suppose this is just the denial stage of grieving, but it's worth recognizing that the people you know feeling this way are working through a process.
Pretending that someone isn't dead isn't a long term solution to accepting loss, even if it means in the short term you are in a dark place emotionally. It's unfortunately it upsets you to see people experiencing this, but those people, given enough time, might be in a better place to help you when you finally have to let go of denial.