Normal developmental stages
It is common and normal for babies to show less interest in breastfeeding sometime during the second six months. This is developmental and not an indication that baby wishes to stop nursing.
Older babies tend to be distractible and want to be a part of all the action around them. Your baby may be more interested in learning about the world than in eating during the day (these same babies often increase their night nursing to make up for their busy days).
If baby is being given a bottle or sippy cup frequently, he discovers that he can walk/crawl around with it and not miss a thing, whereas nursing generally requires sitting still and not looking around for a few minutes. For this reason, some babies develop a preference for the bottle or cup at this developmental stage.
Milestone times, such as crawling and walking, and stressful times like teething or illness can also cause baby to be less interested in nursing - these types of things are common in the second six months. Nursing strikes (when baby quits nursing suddenly) also tend to be more common around this age, perhaps due to the same factors.
Our society tends to produce the expectation that babies can and should become independent as quickly as possible. Babies are considered more independent when they sleep alone, sleep through the night, potty train, wean, etc., As a result, babies are often pushed toward these milestones before they are ready - emotionally or physically. Because of this societal mindset, many moms don't even consider the idea that baby's disinterest in breastfeeding might be temporary, but simply go ahead and wean.
This is not saying that a mother's choice to wean a baby this age is necessarily a bad choice for her family. A mother who wishes to wean her child at this point can certainly take advantage of baby's temporary disinterest in nursing to initiate mother-led weaning.
However, it should understand that this is not self-weaning but a temporary developmental stage. Mom is making the choice, not baby. Once mom knows that she has a choice in the matter, she can better make an informed decision of whether to wean or to seek the benefits of continued nursing.