Why does robin gibb never played instruments on the stage and his name not mentioned on the credits which instruments he played always only vocals?

Robin Gibb, as a member of the Bee Gees, primarily focused on his vocal abilities and songwriting skills rather than playing instruments on stage. His contributions to the group were mainly in the form of lead and backing vocals, as well as songwriting. The credits for the instruments played in their songs typically highlight the instrumentalists who provided accompaniment, rather than the vocalists. This division of roles allowed each member of the band to specialize in their respective talents and create a cohesive sound.