It mainly depends on the very definition of “use”, really.

People use Excel for the simplest thing like making tables of lists of things with some details in a couple of columns, grocery lists and class attedance with no to little, simple formula, to making 5–10 years marketing and sales prediction from hundreds or thousands of data rows and complex relations between columns through an intricately written formulas intertwining a vast arrays of data and tables, coupled with macros to automate the input, analysis processes and output. So we can simply say that they can use Excel. Anyone can use Excel.

But if you ask why not many people know how to exploit Excel’s features and functions to make use of it more . . . well I must agree with Chuck up there. People are comfortable of what they feel familiar with, so they think the way they use Excel is just enough for them. The term used to describe this when I was still a management consultant is unconscious incompetence. They don’t know what awesome things they can do on, with and through Excel. That’s why people mostly experience jawdrop and moments of awe whenever I show them that I can insert other never-seen-before functions into their beloved VLOOKUP function: They simply didn’t even know that we can actually use functions within functions within functions (functionception) other than nested IF. And after that, they usually become SO curious of what else Excel can do, they often come to me asking all kinds of question from simple things to ridiculously difficult and complex tasks they want Excel do.

So, yeah, I guess, why so many people not know how to use Excel, it’s because they simply don’t know what Excel is capable of, they are quite comfortable with the way they usually use Excel. They just need their eyes opened by me, you, any Excel enthusiasts who want to share our knowledge to improve others.