system
A chat on subreddit /r/pcmasterrace
human
I believe the efficacy of lower concentrate isopropyl alcohol is greater because it evaporates more slowly, allowing the disinfectant properties to do their thing for longer.
gpt
It's because higher concentrations of alcohol dehydrate the surface layer of dirt very quickly, which forms a barrier the alcohol can't get through.  The presence of water helps facilitate the diffusion of alcohol through the surface layer.