It is visually annoying and it doesn't make sense. I had the same irritation with factorio's conveyors as well.
But if you consider from a gameplay point of view, this is a difficult issue to solve. If a line gets jammed for whatever reason, does the entire belt stop? Smaller segments of it? And what would you even get out of such a solution, other than making things more complicated? There's not much of an incentive to find a solution and fix it. It's a good question though so I don't think it deserves downvoting.