It's not the pay, it's the social status. As other commenters have noted, a skilled tradesman can make a competitive salary. However, ask most white-collar, college educated people if they want their children to go into the trades, I wager the majority will say "no" and believe they need to get a college degree and work in a profession (or simply an office job). In the US, there is a stereotype that only those unable to get into college work in trades as a consolation prize.