You paid the labor charge for the tech, but you didn't pay for their truck, the fuel, the parts guy ordering the part, that they actually could find the part, the laborer that did receiving at the shop and put the part on the techs truck, etc
The difference is a homeowner thinks the service tech just runs to home Depot and grabs a part.
In reality, we go check out the call. Determine a solution to the problem, call/email the part into the parts guy, parts guy sources it from any number of vendors, get it into stock on the truck, and finally drive out and replace it.
They also forget I'm driving a truck that the company paid $45k for used, will be worth $5k in a few years after I run it up to 4-500k miles, takes a $1500 set of tires every year or less, $200 oil changes every month, random other maintenance and fixes, etc.
It takes money to make money. That's why company's invest millions into their labor force to keep them making millions. However, much of that goes right back out the door. My buddy is small time, 2 employees. He spent $26k in vehicle maintenance, $150k at the parts houses, $140k in wages, $60k in taxes, to make $100k for himself. He still wears a tool belt and does a lot himself. If he hired a 3rd guy to do his job he'd be damn near going backwards.