Because aluminum is literally less durable than steel alloys, and steel chains are way more durable than belts, with a single speed bike. If you leave your bik

Because aluminum is literally less durable than steel alloys, and steel chains are way more durable than belts, with a single speed bike. If you leave your bike out in the elements and don't maintain it, any parts that do not survive prolonged exposure to heat cycle, water, oxidation, salt, etc will deteriorate. But that isn't even metal durability, that's just plain weather. Any bike will deteriorate outside. Another downside is aluminum is stiffer than steel, making for a rougher ride unless you add suspension, get softer tires or significantly change geometry.