An aspiring master would have to pass through the career chain from apprentice to journeyman before he could be elected to become a master craftsman. He would then have to produce a sum of money and a masterpiece before he could actually join the guild. If the masterpiece was not accepted by the masters, he was not allowed to join the guild, possibly remaining a journeyman for the rest of his life. Becoming a master was often very hard.
In many guilds, the master craftsman had strict obligations, one of which was to take on an apprentice (or several depending on the craft) to ensure the survival of the guild.Without apprentices, there would be no one left to continue the craft.
I've often wondered what it would take to join the Lollipop Guild