Why shouldn't store owners be free to decide if they want to open on a Sunday like any other day?
Most can. It only applies to large stores.
Smaller stores usually close because people aren't out in the morning or evening, which you could argue is because the larger shops are closed, or because people are doing other things.
If you are going to see a sporting event, I doubt you're also going to do your weekly shop. I appreciate you're likely talking about more than supermarkets, but the same applies. If I'm going to see football, rugby, a show, the cinema or whatever - am I also going to go to a major shopping centre before or after? Almost certainly not before as you can't take anything bigger than a bit of A4 paper into most venues.
If you mean Sunday amateur football, well, my son played football on a Sunday but that was two hours (including warm-up/training) so we could go shopping after.
If shops were habitually closed every Sunday (The Entertainer seems happy with this) then maybe we could debate, but six hours is quite a long time - and, as I said, smaller shops can legally open but likely are simply choosing not to.
Lots of local pubs had late licences for Friday and Saturday night but since Covid not a one has opened beyond 2300. That is their choice. Even my local kebab van hasn't opened beyond 2330 since Covid, when before he was open until 0200.