They are not supposed to tell us stuff because of the Prime Directive. Duh.
The Prime Directive prohibits Starfleet personnel and spacecraft from interfering in the normal development of any society, and mandates that any Starfleet vessel or crew member is expendable to prevent violation of this rule.
and
As the right of each sentient species to live in accordance with its normal cultural evolution is considered sacred, no Starfleet personnel may interfere with the normal and healthy development of alien life and culture. Such interference includes introducing superior knowledge, strength, or technology to a world whose society is incapable of handling such advantages wisely. Starfleet personnel may not violate this Prime Directive, even to save their lives and/or their ship, unless they are acting to right an earlier violation or an accidental contamination of said culture. This directive takes precedence over any and all other considerations, and carries with it the highest moral obligation