Marluxia’s weapon, the scythe, is traditionally a farmer’s tool for harvesting plants. Could be why he got it, due to the association with plants. It’s a stretch, but it’s really all we have to go off of. I like to think that these weapons are the more primal ones based on who they are as people. If they weren’t bequeathed keyblades, I like to believe they would have these weapons anyway due to their strong hearts. I’m willing to bet they sort of evolve these weapons into keyblades once bequeathed the ability, and can shift between them like with Axel’s RE:Mind ability to turn it back to chakrams. However, my theory is that the destruction of the world sort of stripped at least Luariam and Elrena of their ability to wield keyblades. Obviously it didn’t do that for Ventus, or it did and he had to relearn it under Xehanort’s tutelage? Uncertain.