Dear Mdd,
Because there is more to Torah than just prattling about what type of hat and coat moshiach will wear. Or which language do the gods converse in.
Do you even realize what you are insinuating? According to your take, a true Jewish form of Christianity would not be worth making trouble over. Just take out the traces of paganism and we are good to go!
Let’s throw it back to you. Why were Yidden going to be killed instead of accepting Islam?!?!? It is monotheistic with no avodah zara.