My guess would be people have not taken the plunge for reasons not far off from any other person starting a business in general: money, risk, and fear of the unknown (in that order). I'd be willing to bet that on average a homebrewer would much rather jump at the chance to brew professional, than open their own brewpub/brewery. The latter takes much more than just wanting to brew. I love homebrewing and I have been exploring the possibility of opening a brewpub in my area. However, I am aiming more to be a brewpub and business owner, than a brewer. If I was to get serious about it I would hire a brewer with experience. One, because I have no idea how to operate a large scale brewery (or even a 7bbl one for that matter). And two, I think it is asking a bit of oneself to be a brewpub owner and brewer. That's not saying I wouldn't be involved in creating the beers I want served at my place, I just think it's too much for someone to take on. I think owning strictly a brewery and being the brewer is different however, but each poses their own set of unique difficulties.