It obviously didn't get updated to v11.x when most of the other appliances were (early this year). I'm not sure why that is, whether it was just acidentally missed by the devs, or whether there is/was a technical difficulty (as there is with the Zimbra appliance). But as John mentions it is available as a legacy appliance.

Hopefully it will be updated with the next major (v12.x) TKL release (sometime next year). And perhaps we'll hear from the devs in the meantime why this appliance missed a v11.x release.