The reason is simple. Revelation changes or at least upsets everything and almost everybody.
This is certainly the case for founders of religious traditions. The Hebrew prophets were stoned. Jesus was crucified. Mohammad was ridiculed and driven from the city of Mecca. Joseph Smith was assassinated. Sun Myung Moon endured torture and imprisonment.
In short, “Thus saith the Lord” is a life-threatening proclamation.
This is true not only for founders of religious traditions but also for their followers. Those claiming continuing revelation typically earn such titles as heretic, apostate, deceiver, witch, sorcerer, blasphemer, false prophet, liar, cult leader, and Antichrist.
In fighting off new claims, religious traditions generally follow two strategies.
This first is to close off revelation.
Christianity is a case-in-point. The early Church was a maelstrom of competing points of view, self-proclaimed prophets and founders of new sects. Christians agreed that Jesus had overcome death and in one way or another incarnated the living God. They disagreed about almost everything else: strategies of outreach, leadership, worship, church discipline, Jesus’ divine and human nature, and whether they should pray for or condemn Rome.
In this context, a plethora of individuals and groups arose who claimed continuing revelation. Some attracted broad followings. All were eventually branded heretics and many of their “revelations” claimed to supersede Jesus and his teachings. Among the more notorious were: