Since there was no response, I am asking this question a second time. I hope you'll be able to answer.
For STDs such as chlamydia and gonorrhea, I understand that transmission can occur via oral sex and LIVE in the throat. Given these facts, why is transmission via kissing consistently discounted? Is it considered impossible? If so, why?
It is important to make a distinction between chlamydia and gonorrhea infections in the throat as opposed to the mouth (which you do), because these infections do not cause infection in the mouth. Chlamydia and gonorrhea are not transmitted through contact with saliva.
Chlamydia infections of the throat appear to be rarer than gonorrhea throat infections (overall, both are uncommon). This probably has more to do with what areas of the body the infections "like" to reside; they both prefer the genitals and rectum, but chlamydia seems to prefer the genitals and rectum even more.
Chlamydia and gonnorhea are local infections that infect mucous membranes (vagina, rectum, throat), and are present in mucous membrane secretions (vaginal, rectal, throat) and in semen. They are transmitted when an uninfected person's mucous membranes come into contact with the semen or mucous membranes of an infected person.
Chlamydia and gonorrhea are most commonly transmitted during penile-vaginal and penile-anal sex. They are only likely to be transmitted during oral sex when the activity is oral-penile sex. This is because fellatio is the only oral activity where there is direct genital contact with the throat; the urethra of the penis could have direct contact with the throat during oral sex. It is possible, but less likely, that a person's throat could be infected during oral-vaginal or oral-anal contact with an infected person. Chlamydia and gonorrhea are not known to be transmitted from an infected person's throat to the vagina, rectum, or throat of another person (no direct contact with the mucous membranes of the throat, and not transmitted through saliva).
This is difficult to explain, but I hope you get the picture. Common sense doesn't always follow in describing STI transmission because they are all caused by different organisms that can have slight or major variations in how they are transmitted and cause infection.