There have been at least three main contenders for solving the problem of synchronising personal contacts and schedules with messaging platforms; SyncML, CalDAV/CardDAV and Exchange ActiveSync (EAS).
EAS has been, and still is, the champion of these protocols largely because of its wide adoption across handsets and the fact that it is also a solution for mail access and message submission.
SyncML is largely deprecated and struggled to gain traction across handsets; mainly because of a lack of adoption and ambiguity within its specifications.
CalDAV/CardDAV currently seems to be the only open mainstream contender against EAS - but it too is limited in that it does not provide a complete messaging/data solution (ie: a complete solution requires a combination of CalDAV/CardDAV/IMAP and SMTP).
EAS is not without its limitations either. For example, it currently lacks features for sharing and collaboration. Another downside of ActiveSync is that it requires a nominal license fee be payed to Microsoft (paid both by the client implementation and the server implementation).
Because Microsoft (presumably) makes considerable revenue from Exchange ActiveSync connectivity, CalDAV and CardDAV might be viewed less favourably (because they provide similar functionality without the price-tag). As any chef knows; your cake always tastes better than anyone else's - particularly if you make money when everyone takes a bite.
By comparison, Apple has used these protocols integrally in their products - for example, iPhones, Macs, etc. use CalDAV and CardDAV protocols to communicate with iCloud.
Google originally provided CalDAV/CardDAV support, but is depreciating it and are now pushing their Google Calendar API's (possibly to bind their users to their platform).
The Google Calendar API's are (at least against Google's platform) seemingly more robust than their CalDAV and CardDAV implementations.
The Complete Picture
Firstly, most messaging providers/platforms have (or are in the process of having) provisions for CalDAV and CardDAV. A significant driver for this is to accommodate iPhone user connectivity.
But, for CalDAV and CardDAV to compete with ActiveSync, there needs to be some consensus on how to handle messaging data (since the 3 go hand in hand).
Microsoft originally had a basic interface for messaging over DAV in the early days of Hotmail (back when Hotmail was run not run on Windows); something like it could have been applied to solving the CalDAV/CardDAV messaging gap.
The alternative is to present CalDAV/CardDAV/IMAP and SMTP under as a single service to the user (possibly a neat extension to open handsets).
Future of CalDAV and CardDAV
Whilst Microsoft Exchange does not provide CalDAV and CardDAV support, the majority of messaging platforms/providers do.
To aid in the adoption of CalDAV/CardDAV connectivity, ARPDev Pty. Ltd. has released an Open Source CalDav/CardDAV.NET client library that significantly reduced the development effort associated with integration. ARPDev has done this with the intentions of promoting the protocol, largely because it produces software that provides CalDAV/CardDAV support for Microsoft Outlook.
There are also a large array of Open Source libraries available for non-windows platforms.
Either way though, presenting a single/simple interface for configuring a client's messaging and collaboration features is the arguably the most critical factor in determining which of these protocols flourish.