Is because in the end, and often in the act itself ( whichever, choose any ) it is HARMFUL to both the one who does it, to others, and to God ( via a disconnected relationship with ). Sin is not to be avoided because God said so alone, but because it will HURT YOU IN THE LONG RUN personally , and God who created you, who sustains your very breath, doesn't want you to hurt you, it hurts God to see his child suffer in any manner.
Also it's important to know from whence sin came into being: it came into being from a choice to keep it alive rather than to deny it and to trust God. Lucifer, who was created sinless, grew jealous of one whom he thought he was an equal with, one who it turns out was in fact not an equal with him at all, but one who is an equal with the Father. Because of his jealousy, Lucifer harbored sin within himself, a resentment, a lie, that he was being somehow mistreated, that he wasn't receiving his due, that Gods love was unfair because God had meetings with the one but not with him. Did not that other one stand on the right hand of the throne of God as he, Lucifer stood upon the left, did they not have the same ministry to direct the praises of creation towards the Father ? Lucifer cherished his sin, his self deception, his lie........and the rest is as they say history in the making.
Drew, by the very grace of GOD through the blood of Christ Jesus.
"there shall come after us men whom shall garner great wealth using our system, and having done so shall seek to slam the door of prosperity behind them." George Washington