1. Because they NEVER HAD FAITH IN GOD. (can you show me one act of faith they ever accomplished? The complained BEFORE the red sea, The complained BEFORE the manna, then they complained DURING the manna, They complained BEFORE the rock, then complained BEFORE the second rock. Moses being so fed up with their unbelief that it caused him to sin, and miss out on the promise as he died before the entered.)
2. They never stopped having faith in God. THEY NEVER HAD FAITH
Your really going to go there? Judas never had faith. He believed in jesus but he never had faith, he stole from them from day one, he continued in sin, he did not change his life. Jesus in John 6 even made the remark, You saw me feed 5 thousand, but you do not believe in me, you want a handout, not what I came to offer.
If your going to use examples of people who have seen Gods work and love, yet NEVER had faith in God and HIS WORD (SALVATION) to prove one can lose faith. Your in serious trouble.
These are examples of what james talks about. people who believe in God (even demons believe) yet never had faith in God. their faith could not save them, because their faith was not in Christ and the work he came to do. Many people just like them go to church, and appear to be christian, but never have been. Paul spoke about them even in his day, as did peter james and Jude, John speant quite some time talking about them who have never recieved the anointing, and told us point blank. they were never saved.