Because, if you have the font size set to very large, you might have the same "page number" on more than one screen, which would not help you go to a specific part of the book.
Regarding why they display 1046-56, and you only want 1046, why is having more information than you feel you need a problem? Only look at the first number, and ignore the rest, and others of us can use both numbers, if we want.
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