Materials selection for any piece of equipment or a process system is rarely a simple task, unless you are exactly replicating something successful. Often engineers will have a checklist to help them narrow down the choices, eliminating groups of materials that are not suitable for various reasons. Austenitic 300 series stainless steels containing 7-35% nickel will have most if not all of the boxes checked for being suitable where a stainless steel is desired.
Even small quantities of nickel in an application can make a big difference to successful deployment.
Most nickel production is destined for stainless steel. But a significant 8% is used in the production of alloy steels which are needed to deliver specific characteristics for specialised and often critical applications.