A lot of people (me especially) really hate the way they did a lot of the armor and weapons in 5E. You are correct that there's no reason for a rogue to use a shortbow rather than a light crossbow, so long as both options are available. Even an archery based warrior is better using a crossbow until level 5, but at that point investing in Crossbow Master is a good feat choice. The only real reason to do otherwise is for flavor, and some people have a hard time taking sub-optimal choices for flavor reasons.

IMO the crossbow should have been simple weapons (because they really are compared to bows), while the bows should have been martial, and both deal the same damage. The difference between the types would then be primarily the Heavy property. A bow would be better due to the lack of the loading property, but not better before the extra attack becomes available. This means that ranged warriors could use either equally, but would probably just start with a bow, since that's what they'd want at level 5 anyway. Rogues, Clerics, and other non-warrior classes could use crossbows for similar effect, with the loading property not interfering.