Dude, we all waste more than enough time on any given day that we don’t need to worry about the value of losing a half hour to save tens of dollars on our grocery bill. I can’t imagine anyone using a site like this one is particularly worried about lost productivity during their free time.
Getting value for time is productivity. Up to you if value is in money or enjoyment. Your “logic” seems extreme. I’d have to have some irrational hatred for shopping before I’d spend even more on groceries to get someone else to do it. Similarly, I’d have to have some pretty strong feelings to love it so much I’d take a minimum wage job to do it in my spare time. I think the average person is going to fall firmly in the “if shopping for an extra 30 minutes saves me 20 dollars, I’m doing it” camp.