Travis at least had a family and did have an episode or 2 that was all about him. I personally liked his character. It was just a shame that they never did get to develop the rest like they did with the other series. That is partially due to the fact their run was shortened by 3 years. But I think they had a plan for him as with Hoshi but they never got to fully realize it.
No, that assumes they had a consistent plan throughout, which they didn't. The show was retooled from season to season as its ratings fell. I don't think there's ever been a Trek series that felt so different in every single one of its seasons. In the first season, they tried for a smaller, more character-driven ensemble drama with an emphasis on exploration and discovery, and that's where we got a lot of the best character-building for the supporting cast. In the second season, probably under network pressure, they began playing up the action quotient more and the show became more unfocused in its attempts at character exploration (when they did try to do more character-driven pieces, we got misfires like "A Night in Sickbay," "Singularity," and "Vanishing Point," although there were some decent ones like "Stigma" and "First Flight"). Then in season 3 they threw all their original plans out the window and replaced them with the Xindi arc in a grab for ratings, and development of the supporting cast took a back seat to action and serial plotting. And in season 4, with ratings so low that renewal was unlikely, they just went all-out with the continuity porn to satisfy the hardcore fans who were the only ones still watching. Although the season 4 producers actually made a good effort to reverse Travis's decline into obscurity by giving him more to do, particularly in "Demons"/"Terra Prime."