Economist: In general, several apprentices working together produce about the same amount in an hour as a single more highly trained worker  Hence the more highly trained worker can usually command several times the hourly wage of an apprentice  Thus if the apprentice wage is increased, the hourly wages of more highly trained workers will generally rise by a proportionate amount
Ttherefore the reason that more highly trained workers favor an increased apprentice wage is that it would increase their own wages
if a policy change that people support would work in their favor, that is why they support it