That misses the point. The rules that are set allows for quick screening without extensive training. If they were to screen based on appearance and smell they'd need to study each bottle (what if the contents are hidden?) and/or open them to smell. The time the extra screening would take would cause far more of an uproar with people than having to abandon their liquids now.

I'm sure they know they could allow most liquids on safely if they gave staff some extra training and put people through enough extra screening. But would the end result be convenient enough? Probably not.