Stardust....

[jrichreturns]

[Lord Ghidorah]

Sol's little neighborhood is fairly clean now, but that's because it's currently drifting between more congested regions. During trips through arms there's no telling how just much ancient debris gets scooped up.
The Oort Cloud is tiny on a cosmic scale, but depending on what model one uses it reaches a significant percentage to the next closest star. There are more than plenty of snowballs out there to hold onto really interesting dust.

Earth is our home, and we should take care of it, but there is just so much free matter and energy "out there" that not devoting every nation's utmost to a sustained space economy seems wantonly criminal.