I've also wondered why Judaism isn't a choice. I mean, if what I heard/read is correct, Jesus doesn't fit the description of messiah thus it renders Christianity and Islam invalid. If Jesus isn't the messiah and Christianity and Islam say it is then it is a contradiction... They can't both be right!
Btw, I'm not a Jew so I might be totally wrong on this and I just want to bring Judaism into the picture since it has a valid point too. Plus it makes for a more interesting thread.
He is only messiah in christianity