I'll tell you exactly what happened. The fucking idiots who ran the YHWH story for so many centuries, ran out of ways to keep the sheeple in line...and someone broke the mold and started writing softer stuff...stuff that more evolved brains could actually tolerate. Thus, the New Testament was born. A kinder, gentler YHWH, if you will.
Bottom line, you can't have the NT without the OT, and you don't have any more right to declare one outdated over the other than I have a right to ask Zeus to stop throwing lightning bolts at us. It's really about the church leaders more than anything else. They believe they have the rights to dictate meaning from old writings included in the set. They, and only they can cherry pick to their hearts content...Jesus and YHWH be damned.
Example, when Jesus said in Matthew not to preach in the streets, some asshat decided that's not what he meant...yadda, yadda, etc., etc, mumble, mumble razzlefratz...forget the fact that we really have no clue if Jesus said anything, or what it was, or even if he was real.
This will never end. SPAG is the new religion.