Probably because studies show that people who use excel to manage finance end up coming up with different numbers. JP Morgan lost 6 billion because of excel, and these are preventable problems. It's because you aren't codifying your process, you're just memorizing it and trusting that your memory won't change. Trusting that you won't miss a step. The moment you start doing serious calculations on your data you would be better writing some form of software which can actually handle the amount of complexity that you have in your job. Excel is opaque, hard to manage, easy to diverge. The agency I'm at have made a tremendous reduction in errors by migrating away from excel. Sure it's more work nailing down every process, but they are actually nailed down and you can see them and evaluate whether they are actually correct. You won't have multiple competing standards within a business because we can share our processes. If you think excel is enough you're either doing very simple or low risk job, or much more likely you are floating a lot of totally unnecessary and expensive risk. In finance CENTS matter.