You don't necessarily need to be religious to have a belief in the afterlife, or at least a strong enough suspicion of it to want to be respectful. As an analogy, there's some evidence that people form memories when in a coma. Even if you can never prove that an individual is aware of you, it is still compassionate to assume that they can hear what you say about them.

When you were a baby, many people were kind to you in ways that you don't remember. Was that also pointless?

I also think this goes well beyond the relatives. Part of being in a society is caring for one another. Here I am on another continent, and I feel better that these people are taking a moment to mark someone's passing. If it doesn't matter to you, fine, you don't have to do it. But I don't get why you're putting so much energy into being negative about it.