That is a very good question. There are other qualifications that can enable you to have the skills to perform FDD. For example, a CFA charter may be much more powerful to conduct FDD compared to an ACCA (being a registered accountant). Furthermore, being an accountant does not necessarily qualify you to do FDD, as you may be trained only to manage books but not to uncover skeletons, which is more critical for FDD. CFAs are trained to look at the books from an investor stand point of view and they may be the most suited to perform FDD. CFAs however are much more expensive because acquiring this charter requires higher skills and more effort.
I see the same in my work. My interest in the financial DD is more on understanding it, making sure I can work together with the finance department, and ensure they are taking the right approach (not ticking boxes like it is an audit). Their input is important for other functions doing DD