Don't forget that the government wants the 3 tiered system for $$$.
My home state, Illinois, just passed a self distribute law for small breweries. It barely passed. Why did politicians go on record against it? It was not because of lobbyists but because of lost tax money. When a brewery sells its beer to a distributor the transaction is taxed. When the distributor sells that beer to a retailer or bar it is taxed. When the retailer or bar sells it to the final consumer it is taxed again. The same beer is taxed three different times. The government does not want to lose a third of that tax.
And don't forget why distributors were required by law. Before prohibition breweries owned saloons and rented them to people to run it. They were required to sell only that brewery's product. This was banned by law. Also, the government wanted a "buffer" between the evil breweries and the bars to limit influence of the breweries. If they were right, doing away with the 3 tiered system would increase their ability to squash craft breweries.
Personally I don't would like to see distributors being optional for all breweries. The government does not need to tax beer three times. On the other hand, distributors are vital for small craft breweries. Some friends of mine, 3 brothers, just started a brewery and they contracted with a distributor because they need to in order to survive. They all have other full time jobs and do not have time to sell and deliver their beer. One day they hope to be big enough to quite their jobs and only be brewers, but that is a long way off for them.