That works out well for players, who don't have to "waste" an earned skill level on Steward when it could be better used as Pilot or Gun Combat or, well, anything else.
Not so well for people coming at the rules, decades later, trying to make something "realistic" out of the rule set. (See also, the FASA deck plans for the Patrol Cruiser...)
Fortunately, Steward-0 is acceptable (despite LBB5 stating that the default level for all skills is 2 on military ships). So it's an additional duty on military vessels, and somehow the naval personnel who do it teach themselves up to Steward-2 without a formal instruction system or any documentation on their records.
/shrug/