I think it's just the fact that all of those aren't stars, they're galaxies. Galaxies with millions of stars, which probably has billions of planets, and all of that is just in the equivalent of a single pixel on a 1080p wallpaper (or so I've heard)
The universe is so unfathomably huge, it bothers me. There's what we can see, but how much more is there past that? What even is the universe, really? The idea that it just is, and doesn't have a purpose or reason to be, bothers me.
It bothers me that even if I were immortal, I'd never be able to see even a fraction of it. I'd never be able to see that fraction even before it all becomes a complete void of blackness due to redshift and the universe's expansion.
It bothers me because I have to know. I have to know what's out there.There's gotta be something, it can't be as big as it is, and we're the only ones here to experience it.
But it also bothers me, because it might just be that nothing is out there.
I think that's why it bothers me.