That is because morality doesn't come from religion, and certainly not from any scriptures.
I suspect that notions of right and wrong emerged in our species as a matter of biology long before the advent of religion. Capacities for empathy and cooperation, which I believe are at the root of all morality, enabled humans to live in groups which provided advantages to their members in the struggle for survival. It is difficult to conceive of any society, even one as relatively simple as a clan or a tribe, long enduring without behavioral codes which proscribed such antisocial acts as wanton killing, theft, and tresspass on the conjugal rights of others. Through natural selection, empathic and cooperative traits were passed down in ever greater numbers to offspring. We are, in other words, wired to behave socially and thus "morally".
I do not mean to suggest that the biological inclination for "decent" behavior always prevails. Human behavior, which occurs at the intersection of competing drives and situational provocations, is obviously not always moral. And, the most moral course in any situation is not always clear.
Morality moves in a generally more humanistic direction throughout history. Say that morality is on a continuum from animalistic to humanistic. Morality moves steadily towards the humanistic part. You have a block of what is considered morally acceptable for any given time period and that morality is moving forward slowly. Things that were considered ok in the earlier time periods are not ok anymore because that morality has moved forward.
How then do we explain the 20th century? Despite its recency, the 20th was perhaps the least humane epoch in the history of the species. Witness the blood lettings of the First and Second World Wars, the mass murders under Hitler, Stalin, Pol Pot, and Milosevic, the Armenian genocide, the carnage in Rwanda, the terror states in South Africa and the Jim Crow South, to name but a few of its highlights. The 21st century does not appear to have gotten off to a much more promising start.
But, scriptures are very much so a product of the society they were written in. Obviously. That's a given. But than the morality moves forward and what the scriptures say is not acceptable anymore. Thus we have to adjust what the scriptures say to a more humanistic viewpoint because that morality is not there anymore. We don't abandon the scriptures, we simply re-interpret them over and over so that we can still believe the scriptures are right, we just change the meanings of the words. This is why when we look at things like the Old Testament and we see instructions for how to hold slaves, we re-interpret it and say that the OT is not in affect anymore because of the new covenant in the NT. We re-interpret it to fit the morality of the time.
Clerics have occasionally been dragged kicking and screaming to a more modern understanding of scripture. However, have you had a chance to discuss these views with, say, Saint Santorum? Or, perhaps, with one of the Ayatollahs? I think they might disagree with their thrust.
The problem with organized religion, and the reason I think it has most often been a retardant to human progress, is that so many of the faithful continue to view the content of scripture as divinely revealed literal truth. To be sure, interpretation of scripture is an evolving process for many religions (the Talmud, for example, is a compendium of centuries of rabbinical commentaries on the Torah). However, I think precious few of the faithful would agree that the polestar for the process should ever be the "morality of the time." Once one subscribes to the idea that scripture is the revealed word of God, there may still be some room for interpretation, but it becomes very difficult for expedience or human desire to enter the debate on anything approaching an equal footing.
Better, I think, to just jettison religion's baggage, and apply God's gift of reason to the problem of what is right and what is not.