Looking at the Chinese 30xx and 60xx and various low cost offerings from other parts of the world aluminium is everywhere. I understand the convenience aspect of extrusions but even the parts that are made from plate and bar are aluminium. For a manufacturer working with steel shouldn't be a big obstacle and (at least where I live) it's much less expensive. If bolting steel to aluminium were a problem my car would have fallen apart years ago. One thought is aluminium is simply looks better raw.