Coupons often drive sales for items that people usually wouldn’t buy themselves, sometimes even to people that normally wouldn’t shop there; then once they’ve tried something they haven’t had before, the customer is more likely to purchase that again in the future.
Then there’s additional items you add to the order beyond the coupon.
Finally there’s some rather insane profit margins on some of those items. Even with the coupon, they’re still making profit.
I host my own vpn from home, which keeps me behind my pihole(s) and able to access my private services without exposing them to WAN.
Also secures my mobile traffic from snooping/modifying while on public networks.