Because judo makes you a red hot mack daddy! Many sensei feel that "judoka" doesn't adequately convey this. It's the same reason a karate practitioner is called a "pimp" instead of a karateka.
In my experience, this is not uncommon in styles (like Judo) that are also competitive sports. After all, you are "playing" the sport, just as if you were playing basketball. You can choose to use the term Judoka instead if you think it's more elegant.
You ARE called Judoka. Some people use the term "players" to differentiate between competitors and non-competitors, some people are just ignorant, and the final and most disgusting possibility is that some people may actually feel that "judo player" sounds better. It is important to note that every time you say "Judo player" your deity of choice expresses his wrath at the expense of a kitten.
If there was a God, this would be pretty cool, you Judo player. I hate animals! I'm gonna go play some Judo. "Player" does not seem to convey proper respect for the life and death aspects of fighting, but Judo was intended from the start as a modernized style that was a) liberated from the military and religious traditions of MA and b) played as a competitive sport. "Judoka" sounds a little pretentious coming from someone (me, for example) who doesn't know Japanese. Also, in most languages "-a" is feminine, so our friends in many countries may be calling themselves a bunch of girls. What about Japanglish "Judoman / Judowoman" or "Judoist?"
I found this site http://thejudo.com/. I hope this could help you with what you need regarding the art of judo.
