But how will they spend money on R&D and on new robots, if they can't make the money on them due to unemployed people not being able to pay for their products? I.e. if unemployment reaches a certain level, and economy drops to a certain level, business won't be able to earn enough to continue to automate with robots (high initial investment, long term savings), and will be forced to hire people to do those simple jobs (low initial investment, higher long-term cost).
At the time when technological unemployment will have large impact on the demand, most R&D will be already done. Then production costs for these robots will be orders of magnitude lower than paying even minimum wages.