My guess as a layman would be that AFAIK the reaction of alkali ("group 1") metals with water is more violent the further down it's situated in that column in t

My guess as a layman would be that AFAIK the reaction of alkali ("group 1") metals with water is more violent the further down it's situated in that column in the periodic table. Since Na is one down from Li it should react more violently to any water contact (even water vapor in the atmosphere) which would make it inherently more of a safety concern.