In My Traveller Universe, I use Scouts as a sort of good will monitoring system of low population worlds that are not really on the main routes for merchant activity. Their small cargo capacity limits them from handling high needs shipping, but their constant patrolling of the worlds where they put in to keep tabs on things, a finger on the pulse of the world so to speak, allows them to assist the subsector Duke in keeping informed of things happening within his subsector. They're not military, nor are they really government ships per se - they go where they go and report upon what they see. Even scouts who have left the service and flit about in their own scout ship as a mustering out benefit, are required to report on things they see where every they may go. Just seems to be a natural fit for me.Thing you have to remember is that the Scout Service is a Civilian Institute and not a military one. And its main purpose is to deliver mail, explore and update charts. As well as operating in areas that have little access to higher jump range technologies, so it is easier for them to operate whilst keeping costs down.
So keeping up with the fleet isn't their priority, IMHO. Plus, the Navy does make use of its own couriers, which would be more likely to have higher jump drives so they can keep up.