Because heaven doesn't exist. Because heaven and hell are ordeals created to keep the people in line years ago. And it worked hella good.
You mean excluding the religion-justified slavery and tribal systems, the stoning, burnings, murders, and beheadings, oh and of course all of the wars, the crusades, WWII, and killing and maiming that has gone on and still continues to go in the name of a "god", right?
Christians believe if you are good you go to heaven, and if you're bad you go to hell.
Not just go to heaven for no reason.
That's sketchy at best. What denotes good or bad? Morality is fundamentally a human construct. For example: We, as a society, consider cannibalism (Not murder, strictly the eating of humans) "bad", but many older cultures viewed it as recycling, a necessity.
Even more-so, why the forget would Hell exist? Why would a god, that has supposedly transcended human emotion, described as being "all knowing, all loving, and understandable, send a soul to Hell?
EVEN MORE, Hell is a scientific impossibility. Pain is caused by receiving pain through neuro-pathways, so:
A. What about people who don't feel pain? They exist, yes.
B. What about masochists, who thrive on pain?
C. What about the fact that you're loving dead and you don't HAVE any neurons?
That's all ignoring the fact that most Christians haven't actually read the bible and still say Satan is lord of Hell, even though it's clearly outlined that he's the prisoner (and illustrated in the Divine Comedy as frozen in lake Cocytus) and that the AntiChrist is actually anyone who doesn't believe in christ
"Many deceivers, who do not acknowledge Jesus Christ as coming in the flesh, have gone out into the world. Any such person is the deceiver and the Antichrist." (2 John 1:7)
Or even that Angels are definitely not men with wings, and are hardly described in the bible, and when they are they are DEFINITELY not even close to man-like:
Each of the cherubim had four faces: One face was that of a cherub, the second the face of a human being, the third the face of a lion, and the fourth the face of an eagle.