There is no free lunch. Every blue collar business that you can cook up either comes with significant start up costs or a decade of crap jobs working your way up the ladder. The money you make is directly proportional to the amount of stuff you do in house from customer acquisition to maintaining your machines. This comes with employees, paperwork, compliance, etc, etc or it caps your scale.

Those who don't have the equity to buy excavation equipment can also rent it on a per-job basis. That's not really an option with semi trucks?

You can rent 18-wheelers, but the rental price ends up being such that after expenses, you'd be making not much at all (they're aimed at companies).

still need a truck to haul the backhoe around