wastefulness is instant gratification with usually quite a delayed consequence, unless you managed to waste something that you immediately needed
sometimes, the consequences can be so delayed (or minor) that they are basically irrelevant to you

but also, >>6 has it right: a lot of things that seem wasteful aren't
the situation in >>11 is pretty familiar and probably would have been best solved by getting a reusable bag but that might have still seemed like a waste even compared to a thin plastic bag if you didn't expect to need to use it again
personally, I've ended up just taking the bags if I'm carrying stuff