The simple answer is that we aren’t. Religions evolve just like everything else. The Christianity that we follow now is nothing like early Christianity or any other form of it throughout history. The Catholic Church no longer sells indulgences, Buddhists no longer generally adhere to the fundamentals of karma.
All of the other religions are the same way. Religious debates get settled eventually, and it either provokes a split or everyone just decides it’s not important enough and goes with the majority opinion.
There are certain dogmas which have become stronger over time and not less. But even people’s attitudes towards them change over time. Religious folks are like everyone else, they don’t throw out what’s working.