I craft because I have this issue with shinies. I see shinies, I loot shinies. Since my shinies are often of the gem and ore type, it seems only natural that I put this bad habit to good use. I also like being able to craft my own gear, and eso is the one game with a crafting system that is great. In most games, by the time you can craft something you can use, you have out leveled it, or you got a drop that was just as good or better. In eso, since the gear doesn't come with your traditional stats, but minor traits such as crit resistance, attack speed, mundus stone buffs, increased armor, increased armor and spell resistance, increased spell and armor penetration, stuff that you can't really get else where in your character profile, it means crafting the items will mean you can pick the traits you actually want.
On top of that, items that drop, are usually stuff in that quality, and if you craft, you can actually improve the quality of items. I am not sure 100% but I heard that dropped items can only be improved by one quality level, while crafted items can be improved all the way. I can say that I have improved the quality of a drop, as I had a green sword that I enjoyed the 3pc bonus off, and I boosted its quality to a blue which allowed me far more levels out of it than if it was simply a green. I have easily made items as well and improved the quality of them from white to blue, and since I have both black smithing and enchanting, I can pick the trait I want for the items I am crafting, and then turn around and actually put the enchant I want on the item. Some items you get, especially named items from bosses and quests, you can not change the enchant on the item at all. This means, you are either stuck with that item and its undesired enchantment, or you vendor it and wait for something to drop that you will use.
Lastly, the advantage I can say is only available through crafting, even though you can pay others to make them, is crafting a matching set of gear or the look you want. I have seen alot of people in my travels so far that look like hodge podge warriors, with gear from this style or that style and they do not match in the least. These are probably the players who have stuck to the "Only use what I loot" rule and tend to have the rainbow warrior look with mix matched gear. As a crafting, I can easily upgrade my armor, to my level of need, and pick the look that I like best, and craft it. This means that no matter what my level, i will always be in style and having a matching look of armor, thus look cool killing all sorts of mobs, while at the same time being in level appropriate gear (as long as I don't mind being in mostly white quality gear).
So ultimately, you can get good gear from drops, but if you can craft it, you can have good gear, or improve good gear to make the gear you are wearing, better than just relying on that hopeful drop.