In most cities, it’s a mix, but the short answer is that many urban public trash cans are not lined and are instead designed to be hosed out or pressure-washed. Sidewalk bins, park cans, and street-corner containers often go without liners because liners tear easily, get contaminated, and would need to be replaced constantly. Crews usually empty the can into a truck, then clean the inside on a schedule or when it gets dirty.
That said, some busy locations do use heavy-duty liners. You’ll see them more often at transit stations, food courts, event spaces, or places where liquids and messy waste are common. A strong liner can keep the can cleaner and make servicing faster, but it is not universal.
For residential wheeled carts, the same idea applies: they usually don’t come with liners. Some people bag their trash, and some cities will hose out or wash carts occasionally, but the cart itself is generally meant to be emptied and cleaned rather than lined every time.
So if you’re picturing a city worker pulling a fresh bag from every street can, that’s usually not how it works. Most urban cans are built for direct emptying and periodic washing, with liners used only where they make practical sense.