Ah, but it's different businesses. The folks you did hire are making money by not permitting the drains to be obstreperous; they come in, they do it, it is all done, we do another one in the afternoon, they work as steadily as they can arrange, and they work at fairly low margins per job but that's OK because they try to be busy all the time.

Roto-rooter make money by solving emergencies; they're effectively the plumbing equivalent of the fire department. They maintain not-currently-busy equipment so they can show up Right Now when someone's basement is in doubtful or drastic condition and they're (probably) much better at rapid excavation than they are at relining. (Much like the fire department absolutely will get your door open, but are not the folks you want to have fix a squeaky hinge.) If you haven't got the cash on hand, well, someone ELSE has their basement apparently directly connected to an abattoir in Mordor and they do have the cash. (Maybe today, maybe tomorrow; with what they charge, that's a viable business model.) Specialists in efficiency rather than availability worry about financing, because they need to keep busy all the time. Roto-rooter is a specialist in solving the problems of someone with glassy eyes, a disturbed repeating mutter about how it's all full, and a willingness to hand over a cheque right then rather than think about the particulars of full any more.