(Fiction) Possible reasons the current population got wiped out
This is for purely fictional scenarios, feel free to add / branch this if you find it interesting.
1. Meteor crashing into earth
A meteor of 1km diameter would plunge earth into total darkness, with debris that stopped the sun from reaching the earth's surface, therefore the end of the current civilization
2. Climate catastrophy
Increased extinction, in the end almost everything on earth died. Earth had reached the maximum population, thus what's left is trash and more trash, but everything else is intact.
3. Nuclear war
An atomic reaction that wiped out most living being on this planet (Though it needs to be an all out war, and there might be leftover population - people who survived in bunkers)
4. Global disease that kills most
It's like the bubonic plague but more deadly. Again, we'll have so many abandoned buildings and trash.
5. Volcano eruptions, tectonic plates moving
It would wipe out parts of the world, but not sure if the entire planet will feel it.
6. The sun died
It will cause the planet crashing into each other, and won't make it feasible to restart the life.
7. The sun power was interrupted
More interesting, although not sure why this happened. Maybe super low solar flares? Things could resume when the sun is out again, though everything else must've died.
8. Alien invasion
9. Robot / AI takes over
A megalomaniac billionaire kept developing technology that would accidentally wipe out everything.