The atf is both a lubricant that helps a cleaning brush or scrubbing material move through the bore, it also keeps dislodged crud in suspension, and is also a rust preventative, though the latter quality is not really needed but doesn't hurt to have. I'm sure common motor oil could be used if atf feels like overkill. The acetone or lacquer thinner is an aggressive solvent that breaks down plastic wad residue really well. Kerosene doesn't do that, not to mention that true old-fashioned "coal oil" kerosene is not that readily available these days.
It's good practice to keep anything that will harm your stock finish away from the stock.
JR
