This is the ex post facto rationalization of the rules, not the actual reason. The actual reason is that businesses are more likely to have contracted it out regardless so are less likely to oppose, and are the more lucrative customers for the license holders lobbying for the rules, whereas homeowners object more and have a larger voting block.

Notice that the rules are based on use and not occupancy. A residential multi-unit condo will have more occupants than a small business that only serves five customers at once.

Meanwhile nobody actually wants an electrical fire. The primary thing leading to shoddy workmanship is artificial supply constraints on professional work, which creates financial pressure for amateurs to covertly perform work they're not qualified to do because there aren't enough professionals and puts the professionals under time pressure because there is too much work for them to complete with that number of workers.