I've got a plausible theory how that happend:

In many European countries a lot of charities used to collect bottle tops and sell them for fiat - this is the best type of plastic, thick, unified in colour, can be easily recycled - so there is a market for it. So I think it's the big recycling companies just trying to extract more money out of their operations (many more bottle tops end up in their hands) under false pretends that it's all about saving the planet...