They may have evolved that way, but I belong to several informal guilds, and they are very different than the modern union. We collaborate, swap labour, share information, train apprentices and engage in brotherhood activities. But we don’t organize for mass action, and we certainly don’t try to fix prices. We also have open door policies. Anyone can come and go as they please. There may be membership applications, but there is no contract to remain in the guild or vote taking process on action. Each guild is run privately by an interested party with a profit motive.
Of course, we’re in industries with lots of competition, and people who are not competent are not very prominent in the guild. The most capable people are the most respected, and thus the ones in leadership positions.