In that case why offer the service at all? Or not have a minimum order? Or why not add a delivery charge?
Presumably you don't do supermarket shopping online.
They offer the service because the others do. The first one to end it would lose huge numbers of customers to competitors and ultimately it may even out, but it would be a huge risk.
They do have a minimum order Tesco is £40, which I think is pretty standard.
They do have a delivery charge, either a charge per dlot which varies with the popularity of the day and time, or a season ticket - pay x per month for unlimited deliveries. I pay Tesco £6.99 a month. I believe new customers pay more but I have been using them for a long time (pre-Covid) and they have not increased the price for existing customers.
The benefits to me are huge:
transport costs - when I started I didn't have a car so took the bus there, did a huge monthly shop and paid for a taxi home. Now I have a car I would have gone more than once a week, so big transport cost savings
time and convenience - start the shopping list every week to reserve the slot and add to it as I think of things needed. You can't do that in a supermarket.
spending - no impulse buying, because you only see what you are looking for. For me, this is the biggest saving and it must be costing the supermarkets a fortune. They are trying to get round that by inserting various offers and enticements - it takes about 5 screens to check out as they try to get you to buy more, but it is easier to ignore online than instore.
If Tesco withdrew this service I would go elsewhere, even if I ended up paying more because I hate (and always have hated) supermarket shopping.