Don't worry, you will be able to buy this exact same game for 60$ per year for eternity now
The rest of the Dirt series (same name, very different game) might continue to exist to complement their NFS car game lineup.
Most likely though is that EA only wanted the licenses to F1 and WRC series.
Typical.
Also, all these things are one day trials...that have to be used within 7 days or they expire.