Junior site supervisors are entry level management positions. Comparing Apples and Dugongs. Seriously it does get hilarious the comparisons here. You'd have to been in the trade for a few years and hold some form of management qualification to be considered as well as show leadership and management traits. You might get a much lower paid supervisor role on half the money with lower quals, but those $100k plus paying jobs are multiple sites over $2mil values.
Like saying the store manager at coles earns $100k a year vs a captain at an airline, when the comparative role within the company is a checkout operator supervisor (who earns $1 per hour more than the check out operator).