They own the trucks and equipment now
How did they get the money to buy the trucks and equipment?
sjames makes a huge deal over the "million dollar daddy" but for everyone who starts a company who doesn't have rich parents to mooch from, the answer is that the founder had a previous job from which they saved money before starting their company. If the master plumber automates their work, then they no longer need to hire apprentice plumbers, and the next generation of plumbers will no longer have a job from which they can save up money to start their own shop.
Personally, though, I don't see this will become a permanent problem without a major libertarian takeover of the country. Reason: your factory full of robots has a nonzero property value, and therefore is subject to property tax. At some point, hiring a human will cost less than the property tax on your robot, especially as the monetary value of the robots' output falls. Of course, that supposes that the robots don't start assembling themselves causing their own cost to drop. In that case, with a major libertarian takeover of the country, people could sell a blowjob or two to raise the capital to buy a robot (unless someone invents a robot that gives killer blowjobs).