1. Lore. Obviously, darts were ... weird. While we can say today that they were modeled after Roman War Darts (Plumbata) ... we didn't know that then. To us, darts were things you played with in the rec room or at bars. They weren't combat weapons. Conceptually, the idea of a MU using darts seemed stupid to us, since it wasn't something that was ever within any fiction we had come across.
Well, not to share yet another thing from the past that many will say did not exist or they never even heard of where they grew up.......but we did have Lawn Darts. And, no, not the safe Nerf ones you can buy at Wal Mart today. We had plastic fins...with weighted long metal spikes. They were exactly as dangerous as they sound.
Also, depending on the location, a lot of American tribes used lots of "small, sharp pointed, hand thrown weapons"..
I've always had more "primitive" magic users take darts. And a couple others, just to stay out of melee. Pure elf magic users used darts too.
Also, I have found that 5e is much more focused on roleplaying than on combat (4e would be your most combat-oriented edition, IMO). This may be less about the rules than the culture, though, as the rise of actual play shows has effectively acculturated a mass audience towards heavy RP.
And I find it to be 100% opposite. 5E is all about rolling dice and skipping all role playing.
When a 5E game has something like "two half orc guards by a back door", the players need not even look up from their phones as they roll. The player mubles they got like a 30 for a DC of 10, and the DM just says "wow...you..um..somehow..got past the guards". And the players just nod a bit.
In The Before Time, there were not very many such rules. Not in the offical rules. Sure there where lots of stuff floating around....but not in the rules. Players had to ACT, that is role play their character, for REAL and craft a REAL life way, in the game, to get past the guards. Players would come up with all sorts of REAL role playing ways using no rules or dice, to get past such things.
And this is quite on display in my games with "other" players that are not part of my gamer pool. As I ask for descriptions of "what your character is doing". And most of the "other" gamers will answer with "Aww, come on DM I don't know how to make a fire...but my super smart character rolled a 18. Can't we just say he does it?'
And when you Role Play Act for Real, there is always a chance of something happening...up to and including character death. When the sneak is caught in 5E they just roll a "whatever whatever check" and "alter reality" and are let go. In the old days the player would have to speak in character and come up with a story or explanation. And if they name dropped the wrong NPC or said the wrong things...the character would be killed right there.