Probably because they are entirely different jobs. The “tradesmen” making the big bucks are actually business owners, who are hiring others to clean the toilets and wire circuit breakers. This makes them more like CEOs than individual plumbers. It would not make sense to lump their salaries with employed trade workers.
The last plumber I hired was two brothers, who do good work, charge like $100+/hr on labor, but are considered self employed and thus don't show up in that dataset.
And I’d bet their rate even has to take into account the time in their “off” hours when they are writing estimates, invoicing, communicating with clients, marketing, and so forth.
They don’t just clock out when they finish fixing your plumbing. Even at $100 each, it’s not pure profit. Running the business probably eats into a big chunk of their hourly rate.