I know no-one here is saying it, but I think some of the appeal of 'craft' or 'micro' breweries lies in the idea that smaller brewery = better beer. Which I think is not really justified (I'm talking about real ale here, not A-B Budweiser, John Smith's Extra Smooth or any of that bollocks). Case in point: Tim Taylor Landlord is a pretty mainstream ale now, having been relatively obscure a decade or so ago, and I still think it's pretty good. London Pride and Young's Bitter (their regular 3.7% one) are very, very drinkable when they're kept well; Fuller's London Porter is one of the best black beers going, IMO; Sam Smith's is another pretty decent mid-sized brewery. OTOH some of the worst beers I've tasted have come from the much smaller Cottage brewery - but then, all their pump clips are decorated with charmingly naff paintings of steam trains and have names like Heavy Gauge or Flying Scotsman, so they're clearly going for the unironically-bearded market. It's very much 'real ale' as opposed to 'craft beer', in other words.
That's not to say there aren't some genuinely excellent smaller brewers, obviously. Phoenix (I know Scott's with me on this one), Hopback, O'Hanlons - no idea why these guys aren't more well known, most of their beers are available bottle-condition too so there's no reason they shouldn't be in supermarkets and specialist offies up and down the country.