When you run validator nodes, it comes with costs. Staking providers charge a service fee for offering this service, and it can be anywhere from 0% to 100%. The MultiversX Foundation's service fee is 10%. So, if, for example, there are 10 EGLD in rewards for an epoch and the service fee is 10%, the staking contract owner gets 1 EGLD, and the rest (9 EGLD) goes to the delegators.