Because it happened so. Seriously, not every girl after medical school will go to work in the male team of surgeons who joke about penises. And if you think that doctors stop joking about penises in the 2nd year, then you are wrong.
Why do men choose urology? And why do they go to carpenters, cooks? Because it's interesting, everything is pretty commonplace. Yes, the study and treatment of the genitourinary system can be interesting. Well, money, how could I forget about it. A man will give everything to remain a man.
I would like to add that urology is not only a treatment of the genitourinary system of men. Urologists also treat women's urinary systems (cystitis, for example, is not uncommon)
By the end of their studies at the medical school, the administration arranges students in three slender columns: therapists, surgeons and obstetrician-gynecologists. then a narrow specialization begins in the internship. Doctors are engaged in urology who have chosen a surgical field of activity. With your own hands, without blood and a scalpel, you can massage the prostate gland and insert the catheter into the urethra. To remove stones from the urine of the excretory tract, which cannot be crushed with the help of modern equipment, to perform circumcision, is possible only in the old fashioned way, with the help of a scalpel, i.e. promptly. Don't forget about the psychological component of your question. Imagine a man who comes for a prostate massage, and he is greeted by a tall blonde 90-60-90 on her right hand with a rubber glove, the index finger of which is abundantly greased with Vaseline.