[kazinator]

Because with welding, you can build useful frame structures out of tubes and rods.

Would you ride a bike frame forged by a blacksmith? Haha.

[dreamcompiler]

I don't understand your point. Do you think blacksmiths cannot forge tubes? Who do you think made the first guns? Or bicycles for that matter?

A bike frame forged by a blacksmith would be incredibly strong but it would also be an enormous amount of work.