I often suggest that a cup of water is offered when babies start solids at 6 months or after. At the start it's a learning experience - more gets sprinkled on themselves than goes in the mouth. However you have kinda hit the nail on the head. Babies don't "self wean" at that age - and most mothers who feed to the WHO 2 years or beyond know that 12 mnth olds feed - a lot. And that's the way that breastfeeding is best sustained. However, when babies are denied breastfeeds (schedules, or ideas that they "should only have 4/3/2 breastfeeds per day (name a number) then they of course have to make other arrangements.....and they do. They eat more and drink more, and then breastfeeding becomes a dry argument - they need to eat and mum's supply just isn't there.
Along with this, people also mistake periods of less interest in breastfeeding as being a sign of weaning - when it probably just means that babies are busy and distracted.
So, you have hit on the key for long and successful breastfeeding - feed according to your baby's needs (physical and emotional)