When formula became the norm, and babyfeeding became medicalised - formula just couldn't (in those days at least) sustain a baby to their weaning norm, so you had to add orange juice and solids early to compensate.
I just checked my 'The Modern Womans Home Doctor' and it says that weaning should never be started earlier than 9 months, and that you should even delay that if you would be weaning at the height of summer. Its 1920's by the pictures. By the 1940's the "Everybodys best friend' tells me that 'many modern women resent being tied to their babies for 9 months or longer and give up at 6 months. They are foolish...'