With all the Irwin Allen mockery, there's a semi-serious question that arises when you look at his filmography: why do producers make such bad directors? Allen started as a producer, moved into directing, found success when he stopped directing and stuck to producing, and finally humiliated himself completely when he returned to directing for The Swarm and Beyond the Poseidon Adventure.
There's a long-established history of producers, including many better producers than Irwin Allen, proving to be bad directors. Irwin Winkler may be the best-known example of a good producer who made a bad director. Stanley Kramer had more success as a director, but even his supporters and friends admitted that he wasn't a particularly talented director.
Gabriel Pascal is another one of the classic examples: after Pygmalion was a success he took over directing for the follow-up Shaw adaptation, Major Barbara, and came up with a movie that was not as good or as successful as its predecessor. And even on Broadway, producers have a bad track record when they try to direct: the producing team of Feuer and Martin (Guys and Dolls, How to Succeed) was the most successful in the business until Cy Feuer started directing their shows himself, at which point they started flopping.
Now obviously there have been some producers who made good directors. Alan Pakula did all right, at least for a while. And Joseph L. Mankiewicz was mostly a producer before he started, as was Albert Lewin. But both Mankiewicz and Lewin were screenwriters long before they started producing, so they might be more correctly pegged as writers-turned-directors.
So why is it that there are many successful writers-turned-directors, but very few successful producers-turned-directors? I guess that the easiest answer is that producing and directing require different skills, but then why is it that there are so many directors who successfully become their own producers? The reason directors start producing is that they want to have more control over their films (in studio-system Hollywood, where producers held the power, any director who was any kind of auteur would want to produce his own movies eventually). But theoretically, the same thing could apply to producers; the reason Stanley Kramer started directing his own movies is that he wanted fuller control over the way his movies came out. And a producer has to have experience with many of the elements of filmmaking, probably more than the average screenwriter does; yet it seems like a screenwriter who mostly knows writing is more likely to be a good director than a producer who understands editing, dealing with actors, dealing with technicians, etc. So what is it that makes most producers unable to transition into directing?
Of course the movie The Bad and the Beautiful deals directly with this issue by showing what happens when Selznick-esque producer Jonathan Shields (Kirk Douglas) starts directing for himself. The movie portrays him as a genius producer whose movies are far more his own than the director's, yet when he acts as both producer and director, even though he's well-liked as a director ("thoughtful and considerate" to the crew) the result has "no pace, no tension, nothing." But the movie never gives a clear explanation for why a producer can't direct, except for the cryptic line from the director who quits Shields's film: "To direct a picture, a man needs humility. Do you have humility, Mr. Shields?"