Hmm. Knowing from where I work (in Alberta) this is not true in a general sense.
I’m sure you can make a very good money as an entrepeneur in plumbing (same as in any other possible trade in the world) if you have the wits, you are lucky, you are at the right place at the right time, etc.
But changing whatever office work for whatever physical work, and to move let’s say up north into the oilsands and live there in a camp (the better accomodations have Jack ‘n’ Jill bathroom meaning you have to share bathroom with one other guy - and this is luxury already). Yes true life expenses are paid, plus you can’t spend because there is nowhere to spend. But still.
It’s certainly another thing if you own the business and it’s successful. But if one is not capable of doing the “big jump” (sorry I don’t know the right English expression) as an analyst, accountant, whatever similar - no guarantee you will do better as a plumber.