Craft brewers are not in strict competition with all other craft brewers for the whole market. They would have to expand their operations immensely to do so (and likely no longer be considered "craft"). If I want a pilsner with more or less hop, a smooth saison, or a high-alcohol belgian-style wheat beer, no craft brewer I know of can afford to serve all of these whims. That said, a craft brewer could seek a local monopoly on the citrusy saison, and collaborate to serve different niches.

Craft brewing is almost defined by a premium on variety, and that marketable variety creates an highly recursive system of market segmentation. Since flavour/atmosphere/taste has so many facets, and there is so much variance in terms of "customer success", all product categories which are differentiated by flavour and/or atmosphere and/or taste tend to multiply markets rather than consolidating them. Coca-Cola, for example, could be seen to have no competition at one level (the market for Coca-Cola specifically), and enormous competition (the market for all beverages). Legal restrictions on transportation and processing of raw coca leaf, and on marketing products as "Coca-Cola", help the Coca-Cola company retain a monopoly on Coca-Cola specifically.