That's because there is no RIA Services implementation for WPF (ie. the proper .NET framework).
In the context of WPF, WCF Data Services is nearest of kin in terms of what it is used for, but it's not compatible.
Furthermore, RIA Services is async-only (but doesn't support the async/await paradigm natively), whereas Entity Framework is sync-only (async support comes in EF6 I believe).