That was the motivation as well when the 9€ minimum wage was passed here, too, but they've removed all of them since.
Cashiers are much faster than self checkout, and you still need to employ one person for every 4 self checkouts to prevent theft.
Not to mentioned Ontario, where I'm from, just passed new minimum wage laws ($15CAD/hr) and a bunch of retailers are responding by investing in self checkout for the first time.