How are books made? If by hand: this could also be done by magic then. Same goes for brooms.

Creating things (magically or not) takes time and skill. There’s a finite amount of time that can be spent on honing one’s craft, so societal division of labour makes sense.

As a muggle, I could grow all my own food and sew all my own clothes, but I don’t do that, and neither do most muggles.

I think it seems natural for specialization of skills to arise in wizarding society too.