It matters that I'm not going to interact with them again (or with their dead bodies). For people who are still entangled with me, like tourists in Greece, I allow more grief because in principle my grief (and by TDT-like reasoning, the grief of others) may help prevent other drowning accidents in the future. But you're right that the actual grief I experience in practice for tourists drowning in Greece is for practical purposes zero.

The example of a spaceship is esoteric; I wasn't the one who chose it, but I responded to people discussing exotic propositions like grieving for "acausal" people like those in other quantum branches. I can't even afford to grieve for everyone who suffers on this Earth, in my own branch - 150,000 people die daily and I haven't got that much grief to spend even if I tried to grieve as much as possible (which I don't want to).