Broadly speaking it is down to the bean counters from the goverment down to us, yes even us. Again broadly speaking every year we all need more money and for some time now the goverment has been squeezing councils until the pips burst so departments such as refuse collection have made alterations.
Gone are the weekly bin collections and some councils happily gave contracts to companies to carry out the service for them and allowed these companies to set out a list of things that they charge for which some people object to and found other ways of disposing of their rubbish. Tradepeople now need a waste carriers licence for anything bigger than a sandwich bag found in their van and when they do go to refuse collection points the costs have increased by a large amount of late and that is passed on to the customer ie you and I.
There has always been cowboy fly tippers but because of the above reasons it has now become worse and as for which type of plastic can go where, well not all plastics are the same and to get people to comply they can and do fine us which kind of takes us back to the start.