The Trust does not need people, nor is it worth letting outside influences get a toe hold. If we want more people, we let Midgard roll back their population control measures a bit.
Yeah, no one from the Trust wants to come live on Avernus, but given that we're sitting at 10 billion people we don't need a fucking security leak for an incidental boost to our growth rate. Plus, immigrants AREN'T Avernites—they won't have the cultural and genetic advantages we've built up over the last century or so. If we have enough of them for a measureable bump in quantity, we'll end up suffering a similar drop in quality.
Also, remember that we've been shipping people out to Byzantium for the last few decades. Once we finish that (which will be soon) our population growth rate should go back up.
Honestly speaking, I don't think we should be spending our own political capital on the specifics of any potential trade deal with the other factions. I certainly wouldn't be opposed to Trust members trading the relatively trustworthy (heh) locals Imperial-era ships or some of the economy boosters, but frankly speaking Dragon's Nest and the like are unlikely to have much to offer us that would even be worth our while.