Regardless of whatever happens in that 1000+ years, Goku has still cut down that opportunity. Yes you being erased and the world being erased aren't the same thing, but to one's perspective, simply you being erased vs everything being erased is the same experience. You still end up in nothingness either way, and for you it wouldn't "matter" if you are erased or if everything is erased, because you're nothing anyway. You won't percieve anything at that point.
It mattered because it was relevant to your belief of "nothing matters if everything is erased". Naturally I bring in real life because that's the basis we often use to impose standards (to some extent) when judging fiction.
And you're saying nothing matters if everything is erased in the sense that nothing you did before will "live" if everything is erased. I'm saying the current waking moments of life matter and it's worth enjoying regardless of what happens at the end. That's why that 1000+ years of life matters regardless of if it was going to be erased at the end, and why people have a right to be mad at Goku since their experience is getting cut short because of him.
