Sainsburys have just put up their minimum spend for a delivery (even with a pass) to £50. It's currently £40, so that's a sizeable increase.
I spend more than that, but there are two of us and I buy more than groceries (eg cleaning products etc). Someone living alone might struggle to spend £50, and if you pay £80 for a delivery pass it's not unreasonable to expect free deliveries to be reasonably unconditional. Maybe not regular deliveries of single items, but a weekly delivery is a reasonable expectation, I think.
A single person on a budget might find £50 too much to spend, as well as not needing £50 worth of food. Yes, they could shop less frequently, but then they wouldn't be getting fresh food.