Q. Why don’t we modernise the prayerbook?
A. A person was studying a page of the Talmud. A friend saw what he was doing and noticed which page it was. A week later the same friend came by and was astounded to find that it was still the same page that was open. “Haven’t you moved on?” he asked. “Moved on?” came the reply; “Why should I move on? I like it here!”
Now something which actually happened to me when I was a professional youth worker. When a group of teenagers objected to the conventional Shabbat services because they were boring, they said they wanted to create their own service. I said, “Go ahead!”
They sat and thought and planned and got busy. One suggested this change, another suggested that one. Eventually they were ready to conduct their service. I said nothing aloud but I grinned inwardly when the service they produced was identical to the standard Shabbat service!
Both stories show you get used to certain ways of doing things and in time they define who you are and what you stand for. Changing the Siddur has been tried in non-Orthodox movements but without dramatically better results than the prayerbook of tradition.
True, they have shortened the services and brought in more vernacular prayers, but if they had worked from within the halachah they could have found halachically sanctioned ways of addressing the same issues.
In some cases they have changed the theology, for instance by rejecting references to a personal Messiah, resurrection of the dead and the rebuilding of the Temple, but on most of these questions their own adherents are apathetic.
Recent attempts to rework the Siddur have tried to be gender inclusive, though I cannot see how it is an improvement to refer to God without Biblical terms like “Father” and “Lord”.
We are moulded by our history and tradition, and if this is how Jews have always spoken of God it is part of our identity.