“Stainless steel” refers to a group of metals that meet certain criteria but can vary in exact composition. Some of the metals that fall under the heading “stainless steel” are not magnetic, while others are.
Almost all of our stainless steel tools are composed of magnetic stainless steel because it allows us to use a process of heat treating the steel to achieve specific levels of hardness. The exact hardness of steel used is determined by the function of the tool—anything that cuts, for example, requires harder steel than anything that does not.
Non-magnetic stainless steel cannot be heat treated, and therefore cannot achieve our required specific levels of hardness.