"Si collects data in the present moment and compares it with past experiences, a process that sometimes evokes the feelings associated with memory, as if the subject were reliving it. Seeking to protect what is familiar, Si draws upon history to form goals and expectations about what will happen in the future." Wiki
Why is it that the Si function must "protect what is familiar"? Maybe it has something to do with the inferior function of Si-dom types, which is the Ne function.
"Ne finds and interprets hidden meanings, using 'what if' questions to explore alternatives, allowing multiple possibilities to coexist. This imaginative play weaves together insights and experiences from various sources to form a new whole, which can then become a catalyst to action." Wiki
This is exactly what Si doesn't want. There can be no imaginative interplay of alternatives. There is the right way, and then there is the wrong way. There can be no new whole, only what has been.
That's not to say that the Si-dom is afraid of new things. You will find them investing in new products and inventions all the time. But there won't be any new principles or paradigms to be found anywhere near the Si-dom.