Comment by ars
It's most common in places with lots of elderly or homeless, both groups find these carts very useful and will simply take them, homeless to keep, elderly to abandon near their home once they have transported their groceries.
It's more also common in places where people walk, since it can be hard to bring groceries home on public transport.
So yes, very localized.
The shop near me doesn't have locking wheels (they used to, but stopped), instead they have a guy in a pickup that drives around occasionally, searching for carts.
I understand about homeless people but elderly? Don't they have personnal shopping trolley? Like those with 3 wheels to be able to go climb curbs and small stairs? Regular carts are only used inside or by people who need to bring their stuff to their car and a pain in the ass to operate in the streets as they don't climb curbs easily.
Locally all supermarkets actually have locks at the entrace so that people can lock their shopping trolleys next to the cashiers.