Development of the XDS Connector was initiated back in 2014 and the developer who initiated the project back then had expertise in working with Spring. Not sure what the status of the JAX WS RI was in 2014? Anyway, you can say that it’s partly for historical reasons , partly it’s due to personal preferences/expertise. Several different developers have since then been involved in minor or major increments of the development of this component and, even if some may have favored a JAX WS RI approach, building on top of the existing has been favored over starting all over.
/Michael