Rousey is a world class competitor. She is undefeated in the UFC and was even recently named "athlete of the year". What compels her to leave the fighting world and travel to Hollywood? She had a small supporting role in Fast 7, and while she was well prepared for the fight scenes, her acting was absolutely terrible.
Rousey is not alone in her jump from the Octagon to the silver screen. From Michael Jordan in Space Jam, OJ Simpson in The Naked Gun 2 1/2: Smell the Fear, or Arnold Schwarzenegger in The Terminator; the list goes on and on. These super athletes certainly weren't hurting financially, so what factors pushed them to leave their dominant position in sports (even temporarily) and take on a role in Hollywood?
It could simply be that since these super-athletes are already household names that everyone knows and loves, making them a big ticket item for producers eager to capture the allure of a big name. A prime example of this is the Expendables films, which boasts an ensemble cast of Hollywood's most badass actors- many of whom were athletes in real life. Along that same vein, perhaps choosing athletes to star in a film is a strategy to peak the curiosity of an audience, evoking a "what is he doing there?" reaction much like the way I reacted to the recent Rousey news.
One group that might be exempt from the issues of the athlete-actor crossover are professional wrestlers. Since the 'sport' they play is a staged event, it makes perfect sense that the athletes would also have an acting career. To me, there really isn't much of a difference anyway. It is all a staged production. This explains the success of actors like Dwayne "The Rock" Johnson in transitioning sole to Hollywood, a feat that no other professional athlete outside of pro wrestling can really claim.
Regardless of how much I complain, I really don't see significant change coming anytime soon. I think the recent trend of athlete-actors is only going to continue to increase. Who knows, some day we might reach a point where these individuals can cross successfully between these two very different worlds; we could watch them at the theaters on Saturday and then again on the field on Sunday.