This so common because it is a common STD and found when unprotected sex occurs. Many people have no access to protection.
Typically, only women experience symptoms associated with Trichomonas infection. Symptoms include inflammation of the cervix (cervicitis), urethra (urethritis), and vagina (vaginitis) which produce an itching or burning sensation. Discomfort may increase during intercourse and urination. There may also be a yellow-green, itchy, frothy, foul-smelling ("fishy" smell) vaginal discharge. In rare cases, lower abdominal pain can occur. Symptoms usually appear in women within 5 to 28 days of exposure. In many cases, men may hold the parasite for some years without any signs (dormant). Some sexual health specialists have stated that the condition can probably be carried in the vagina for years, despite standard tests being negative. While symptoms are most common in women, some men may temporarily exhibit symptoms such as an irritation inside the penis, mild discharge, or slight burning after urination or ejaculation.