For the most part, they only become really respected once they direct films they do not appear in themselves and then can keep up the pace by bringing put more films. This is a large part of why Robert Redford and especially Clint Eastwood are so highly respected. This is not an infallible rule (most of Woody Allen's most respected films were both directed by and starring him), but it's mostly true.
Bradley Cooper is genuinely talented as a director, and Barbra Streisand is quite good (though not brilliant). But all the films they've directed have been star vehicles for themselves, and so they seem like egomaniacs.