The owner wants the maximum ratio of servers to customers possible. In the typical USA system, being paid primarily in tips means the server is highly incentivized to upsell the customer as much as possible and do everything they can to increase the total bill, and therefor increase their tip. Essentially a commissioned sales person but the customer pays the commission.
This is the least efficient way to run a restaurant with regard to staffing.
European restaurants typically use a team service model, which greatly reduces the number of staff needed. Every front of house worker can take orders, make and serve drinks, run food to tables, etc. Instead of checking on the customer every few minutes they rely on the customer to ask if you need something. There is no pressure to run up the bill or clear out quickly in this model.