Germany’s not even religious, what’s with the Blue Laws?

It's actually interesting thing. In some countries the "stores closed on Sunday" is a religious thing, like in Poland. Stores used to be open but it was changed recently because the right wing government pushed for it and most people think it's so that people go to church more.

In Germany it was the other way around: all the stores were only opened Mon-Fri and closed early because everyone just assumed that people working in stores should work the same hours as everyone else. This led to terrible experience for the customers (everyone scrambling to do their shopping on Friday evening, right after work) so they slowly started extending the opening hours and finally allowed stores to open on Saturdays.

In Spain stores are closed on Sunday but again, not because of religious reasons but as "worker's rights" thing. One shopping mall near me tried to extend shopping hours on some days during summer and all the workers complained and threatened a strike. No one wants to work on Sunday here, they prefer to spend time with friends and family.