In Lieu of Writing about Sunak
Since this phenomenon, of leaders who are in fact primarily mascots, is common to both Labour and the Tories, you'd be right in thinking that it has a common cause.
Red Fightback contains Caucuses. The purpose of a Caucus is to provide a forum for members that experience a particular form of oppression to: develop the party's positions relating to that Caucus; advise the party on matters relating to that Caucus; and provide political education, support and community for members.
Currently there are four recognised Caucuses:
Racially Oppressed Caucus
Disability Caucus
Past & Present Sex Workers Caucus