Trade lanes are pointless. Maybe at one stage, they planned them to be raided.
Long, long ago, in a galaxy far, far away, freighters could be attacked, they improved relations between trading partners, and offered a pittance in revenue.
Then times changed and you could no longer attack a trade route, then a further change occurred where the diplomacy benefits disappeared. Thankfully, these benefits seem to have reappeared. I generally run a freighter to the capitols of each civ, not for the gold, obviously, but for the Diplo boost. It isn't much, but something is better than nothing, especially if you're trying to maintain peaceful relations.