Because some people enjoy crafting and have fun with it while leveling. I do.
Whether that makes sense in your book or not, doesn't matter. I'm not rich. But the crafts I make at this point, learnt while leveling with different characters, allow me to not be bothered with dailies to get money. That's good enough for me.
Since this is my first MMO, one of the biggest draws of the game for me was to craft my own gear and weapons. After my main got level 50, I had custom gear in every slot for both my toon and his companion. My main is a level 50 SJ with synthweaving at 400. I have a level 24 IA sniper with cybertech at 400, a level 23 SA with artifice at 400 and I just recently started a sorcerer who has armstech at 100 at level 19. I enjoy crafting a lot. I am able to make mods, crystals, hilts, enhancements, armorings and augments for every single slot, but that's not all, i was able to craft artifact level mods for all the slots, which took some time and money, but it set my main character up quite nicely for end-game activities until I was able to get my hands on Columi, BH, or even Tionese gear. Personally, I like the fact that I have made all my own weapons, armor, and mods for my toons.