Do you have any on-topic arguments for why the bagging policy is unreasonable?

Even if you think that context isn't relevant, the premise of covid spread through surface contamination is still dubious. And even if that risk were credible, I assert that banning reusable bags would still be a dubious measure. Instead of using a grocery bag touched only by myself, they'd have me using grocery bags that have been touched by employees. Employees who've also touched my food, which I touched before them. Food which was probably touched by other customers before me. If surface contamination is a serious concern, the entire premise of a self-service grocery store is fucked and they should stop letting customers inside the store (self-service grocery stores are a 20th century invention; alternative schemes exist. Notably, self-service grocery stores weren't common until years after the Spanish Flu...) Since they haven't done that, it's impossible for me to take their bag ban seriously.