How do you know?
https://www.theguardian.com/us-news/2019/jun/21/us-plastic-r...
Municipal recycling is mostly political window dressing to outright falsehoods.
Compost may be similarly beneficial, depending on public compliance, the market/public need for the compost product, and how efficient a particular region can make their system. It is certainly not a one-size-fits-all kind of deal, and probably is not even worth attempting in some regions.
Your original claim was 'almost all' so if you're just talking about plastic I think I'm quite right to question what you 'heard from the garbage guy'.