There is a ton of case law in pretty much every common law jurisdiction establishing that stuff that is visibly trash-like and abandoned in a public area is fair game.
If the job is redundant because volunteers are doing it than maybe the city should stop paying for it.
These areas are private property: the ends of people’s driveways. The city pays for trash and recycling collection from these areas. The scavengers steal all of the profitable items (mostly metal) from people’s recycling, making the recycling program even more unprofitable than it already is.
They're driving fancy pickup trucks so I wouldn't call them desperate. They are scavengers by choice. They could just as easily pick up a trade and do honest work for a living.
There is absolutely no shortage of work for skilled trades workers. My roommate is a drywall taper and he makes a lot of money. He tells me about how unreliable the other people in his trade are. There is a TON of opportunity for people who work hard and act responsibly.
If the job is redundant because volunteers are doing it than maybe the city should stop paying for it.