Most of the "large" shops (I think there is a square-footage cutoff point) and shopping centres/malls must only open for 6 hours on a Sunday. So the normally 24/7 huge supermarkets that are the size of several football pitches and are usually packed full of people are forced to shut. This means that everyone needs to get out in the 6 hour window, so traffic is insane and the shops themselves are insane because all the shopping that normally happens spread across 24 hours has to be jammed into 6 hours. It is really annoying.
Smaller shops are allowed to stay open, so in the UK we now have a lot of smaller versions of the large 24/7 supermarket chain stores on high-streets that are typically open something like 8am-10pm/11pm/midnight 7 days a week. These are obviously much more popular than local businesses (cheaper, more reliable, loyalty schemes) so all small independent businesses (greengrocers, bakeries, small grocery stores, hardware stores, stationers, newsagents etc) are being forced out of business.
I wish that one day this silliness would be abolished.