I'm not sure times have changed that much. Women, in general, are still
brought up to be giggling, brainless morons. (Watch "Ca$h Cab" if you don't
believe me.)

In the context of this photo, the assumption is that women have
substantially less technical background than men (which is still true), so
if a housewife can read and correctly follow the instructions, the kit's
designers have done their job.