No doubt it was simply the sheer amount of material and/or people he was having to move that was draining his abilities.
Or then people are an important part of his propulsion system, and the greatest effort of all would be to move without any. Why does the Traveler enlist the help of the likes of Kosinski? Is it because he wants to get aboard Starfleet ships specifically? It's difficult to imagine why he would, as any warpship would serve. Is it because he wants clearance to modify the engines? But the modifications appear unnecessary, mere smoke and mirrors to hide the true nature of the Traveling. Probably he just likes company - that is, because he burns it for fuel!