How so? FS-level sharing is easy to use (it's just a drive that's the same on everyone's machine) and the workflow is a lot more efficient if you're using a conventional application to edit the files. It performs pretty well, and integrates nicely with AD/Kerberos for security. As long as there's a decent versioning/backup policy in place (which can be handled by the server admins, users don't have to worry about it) what's the problem?

> Why are people doing so much peer level file sharing anyway? Performance? Security? In a company it would be a lot better to have centralized servers with high availability, probably with some kind of web-based CMS to store files, something like Confluence or Sharepoint.

You have to assume that the majority of Apple's users are home/edu/SMB users, who don't have centralised infrastructure.

They just want to share files between each other, or from a small NAS. Those who have Macs in an enterprise environment likely have a working solution via other methods.

Because not everyone is running a server cabinet filled to the brim with high performance kit and a gigabit internet connection. A lot of small companies have limited resources and limited experience and it turns out that peer level file sharing is the easiest way to do what they need, which is share files between themselves.