It is not necessary that all the time target eNodeB sends dedicated preamble within the handover configuration what the target eNodeB prepares. If you go through the mobilityControlInfo then you will realize that dedicated preamble is taken as an optional element.
As of now, I can realize only two reasons as following:
1. Target eNodeB itself is not configured for the usage of dedicated preambles.
2. Dedicated preamble is not available at the moment when it had received handover request for the UE.
