The plumbing business, at least where I live, is becoming increasingly segmented. I got out of the service-and-repair business some time ago because of the overhead involved, and also because I don't like charging the prices that they charge. I understand their prices are necessary due to the cost of vehicles, training, and above all, advertising. You can't swing a dead cat around here without hitting a plumbing van, so the successful service shops advertise quite a bit. The successful plumbing company will have modern vehicles, clean, well-groomed techs with clean uniforms, a snappy logo, and strong ad presence.
Then there are the drain specialists. To be in this business, you need at least 4 different-sized drain snakes, probably 2 to 3 jetting machines with different capabilities, and drain cameras. The up-front cost is considerable, and all of this equipment requires maintenance. It would be easy to spend $20,000 to outfit one vehicle, although most vehicles wouldn't carry all of this equipment. To do this, you also have to advertise heavily.
Then there's new construction, which is what I do now. I do residential and light commercial new construction, remodel/addition work, and commercial TI's. Advertising is much more low-key, and my guys need to be plumbers rather than salesmen. Quite a bit of technical knowledge is required, much more than you need to know to do service work. I'm a pretty small operator at this point, and will still do occasional repairs for some friends and a few property owners. But I don't advertise to homeowners, and I generally refuse to do service work, mostly because I'm just not set up for it, and it would take time away from the new/remodel work we specialize in.
If it sounds like I'm denigrating service guys and drain cleaners, I don't mean to be. They provide a necessary service, and I've done that type of work also.