Seeing it from the perspective of a network filesystem (WebDAV by itself is a lot more, albeit afaik has never been used seriously as an authoring tool) it is a bit over-engineered, but the real problem (expecially when dealing with CardDAV and CalDAV) is the clients/servers inter-operation, as it looks like no-one is able to respect the RFCs (check the amount of hacks the radicale project or davvy needed to make OSX clients happy, or the differences between lightning, korganizer and so on). So the reason is that my patience ended :)