What makes people separate paper trash from other trash? Is it kindness to nature and the world? Fear of global warming? Maybe it's the comfort of having all your newspapers in one place so you can re-read them more easily?
Let's do a small challenge first and we'll get back to the trash issue in a moment.
For most people recycling and getting rid of trash is a question of comfort and availability combined with knowledge of long term consequences of ones actions. You could say that the long term consequences of global warming is the motivation and the design of trash bins and recycling sites is the size of barriers stopping or helping you to act consciously.
You can lower barriers by designing and arranging your world to support your habit building. I'm using a broad definition of design here. It incorporates things like designing your bus route to support a habit.