Alot of razors are ground with two wheels, one on each side of the razor and the worker moves the razor back and forth. Those lines could be from someone with a not so steady head and shifting the razor or from inconsistency in the wheels as well as other factors. Some newer razors are made from belts, whether it be one on each side or just one free handed. Seems to be easier to get more even grinding when done with two or if machines are controlling the grinding and only doing one side at a time.