It depends on how many spaces the cafe has and how expensive rent is.

If the cafe has plenty of free space, then people working on laptops is extra customers and beneficial. If it has little space, then a person ordering a coffee every two hours is taking away space from more profitable customers who eat, drink and leave in 30 minutes.

Because the owner can't pay rent and wages if all customers sit around the whole day working on their laptops and buying two coffees and a sandwich.

Customers are people who spend money. Someone who bought one coffee, but is taking up a seat all day is not a customer.

It's the owners decision to make. Not mine or yours, it's his/her business. And it's definitely not making everybody happy ;)