Can just anyone come up with a graphic design suitable for purpose? After all, doesn't everyone have some art skills, to varying degrees? Graphic design is not a profession as such - its just a hobby someone is making money out of, isn't it? (by the way the answer is no, it isn't)
How many times have you seen a [small] business with a brand image designed by their spouse, nephew or [insert suitable relative with pretensions to artistic granduer here]?
Is it right?
Of course, if they have the necessary training or experience - no problem,
But if they don't - then the person who has trusted their brand image to them is either a huge gambler, or simply not that bothered...
The adage - if you want a job done properly, then get a professional to do it, is normally a pretty safe bet.