Most of the time, dino bones don't fossilize. And we only find some small fraction of the small fraction that do. But with glass and ceramics the situation is different. Those are stable in almost all conditions, running water excepted. A beach will break down a coke bottle in a few years but if it lands just about anywhere else it has a high chance of lasting basically forever.

If dinosaurs ever became like us, there should be a clear layer in the rock where they started throwing their trash on the ground.

If dinosaurs had changed their environment as much as humans, there would probably be more than the occasional fortuitously preserved corpse or footprint to find.