It is very easy to make one’s own. See:
Why has there been a changed - don’t know but suspect it could be to meet a general desire of customers to have the clusters added.
When clusters first appeared, it seemed to be confined to more premium type brands/mixes. Since then, and possibly that clusters are cheaper to produce, they have become common in many mueslis (and breakfast cereals), rather than just the premium brands/mixes. This is possibly to make the muesli appear more ‘premium’ and meet consumer expectations/tastes. Consumer expectations being conditioned by muesli with clusters being more ‘premium’.
