The c-suite has expanded over the years. Originally you had basically the CEO, COO, and CFO. Next, depending on the industry came the CIO/CTO (IT), CMO (marketing), and CHRO/CPO (HR and Talent). Some organizations have added depending on need c-suite roles for strategy, diversity, safety, client/customer support, etc.
Basically, the c-suite is a little like empire building. If you’re a CEO with a decent head on your shoulders you want to surround yourself with people who complement your lack of certain skill sets, or skill sets that need more emphasis.
Don’t be surprised if you start to see another addition