- Plastics really don't mix well. Even trace amount of a different polymer (those numbers in the bottom) will destroy the strength of a batch of plastic (there is research in this though)
- Recycling is expensive and in an economic battle against new stock (carbon tax?).
Cleaving the bonds to make diesel or feedstock is another option to "recycle" polymers (I dunno why it's not done. energy intensive wrt to oil? Dirty?)
Plastics are amazing... but we really should stop using them altogether except for fringe no alternative cases.
P.S. turns out plastics are bio-degradable by some tough organisms. So there's hope.
It's the equivalent of sweeping all those bags under the rug. They're still out there, just permeating into everything instead of being visible.