Probably becasue potion ingredients are easier to come by and also because you're using more potions than weapons. Also IRL forging is a ratehr lengthy porcess compared to mixing remedies.
I found leveling blacksmithing to be super-trivial, just buy up all the iron ingots and ore, make iron daggers, (enchant them with banish or lifesteal if you can), sell them back, wait 48 hours, repeat. It's easy to get to 100 very quickly with very little gold (3000 or so should be plenty). Leveling alch to 100 on the other hand is a real pain in the butt, especially if you didn't make a habit of picking up every flower you saw. If you decide late that you want to level alchemy it can be a real nightmare to get very deep in.