Those crazy brewers pretty much do whatever they want. No, the straight answer is the brewers like to experiment and innovate. Based on what is currently on tap and how much tank space they have at the time, each brewery might offer a new and exciting small batch brew. If they brew enough, the brewers might share it with the other brew pubs, but that brew pub might, or might not have the tap space to offer that beer at that moment. So the beers offered at each brew pub are constantly changing – which makes it more fun. You never know what small batch ales will be on tap.