so where else is there for them to dump the stuff
Plenty of commercial waste places that will take it – but you pay a fee for disposing of that waste, and as project says, have to be registered to be allowed to carry commercial waste (the fee is pretty small).
It’s purely about cost – dodgy tradespeople will undercut legit ones on price but they won’t be wanting to pay the costs (about £115/ton according to The Apprentice the other week!) so chance it and dump it anywhere.
Incidentally, I was helping my gf clear her parents garage in NZ when we were over there, and was pretty shocked to find that they don’t have council tips for domestic waste at all – you have to go to commercial outfits and pay their rates for any stuff you want to get rid of. They collect big stuff (TVs, fridges, etc) at the kerbside free but only about every 6 months. Makes me appreciate that here you can just go back and forth in the car as much as you like!