The main problem with recycling plastics, and it's a HUGE problem, is having a mixture of different types of plastic. Most of it is polyethylene, fairly easy to recycle IF it's a pure stream, or has minor impurities. But, your milk jug is PE, fine, and the CAP is PP (polypropylene). Coke bottles are PET. Fishing line is nylon.
You get all this crap together and you can't do anything with it but burn it.
Then you have polystyrene, which is usually from packaging, the white foam stuff. Then there is polyurethane, usually foam stuff inside pillows and whatnot or insulation.
And then you have rubber tires, which technically isn't plastic and usually isn't in the same stream. Usually.
Most stuff we put in the recycling bin goes to landfill.