This was the whole issue with allowing guilds in the first place... If you only allow a guild to do a job (legally) and the guild also controls how many members they train and accept... The end result is a labor shortage.
Because it's better for the existing members of the guild.
If they train a large number of new members... they spend time and money on training, and they've increased their competition during bidding which drives down rates.
So instead you train the bare minimum for replacements. This keeps your members' rates high and competition low.
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Any time the "pay is great" but the "process to get it sucks!"... you're seeing this in action. It's not that the process really needs to suck, it's that the process roadblocks are there to maintain high pay for the existing trained members.
If there's one thing monopolies don't like... it's competition. And legally enforced certifications are wonderful monopoly creators if you don't manage them carefully.