This says much about respect and social competence in this society when the first instinct is to mock and abuse someone with different priorities than yours.
service is not something the client has to ask for but something the vendor provides. Just like you hold a door open for someone entering behind you, you provide that service, unasked. Having to ask for service is a failure in itself, it's just "no service".
Typically they need attendant attention, to be reset to be usable. Which makes it rather pointless.
My expectation that checkout lines are to be adequately staffed with cashiers. This is, however, increasingly not a safe assumption, in Germany.
I expect the situation to further deteriorate. As does everything else.
Here there are like 10 self-checkouts per 1 employee and they're just there if the machine gets confused about a weight. It's much better, and faster than waiting in the queue for a manned checkout. I can't imagine wanting to go backward, where's the benefit?