Its not as easy as just "why not put all your liquids on your hold luggage" I work short haul for BA ex LHR and we are forbidden to check any bags in, we have to take everything onboard with us, so whenever we go away (which can be anything upto 3 days) all we are allowed is the basic 100mls.
I feel sorry for the girls who have to pack all their make up into this bag, us guys are lucky enough to just have th basics but even then to save space in my bag im forced to use a stick deoderant which i hate!! but it saves me going through an over priced 100ml spary on one every 2-3 days