system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why can't we recycle the stuff that's sent to landfill?
gpt
There are two reasons, both of which are applicable in many cases:

1) Things that are mixed together are more expensive to take apart.  Aluminum cans are easy to recycle because they are almost pure aluminum.  There is aluminum in food packaging, but it's bonded to paper, plastic, and other non-aluminum things in a way that's hard to undo.

2) Some things are not very valuable, and the energy that would be needed to process them costs more than the output of the process could be sold for (even when the cost of the landfill is included).