it could be loads of reasons woman wants to shop herself but doesn't drive is the usual reason and so they go when man is home from work...he could work shifts, work away all week, work overseas etc
he may be the boyfriend who is staying for the weekened
they may be shopping before going away
etcetc
they want saturday and sunday free of shopping chores
they have visitors coming first thing on sat
lots of people like doing things together..dp and i always shop together even though we are both capable of doing it apart, it's boring so we do it together and chat about what we are getting