Why no \new Score?

[Trevor Daniels]

I am writing part of the GDP Learning Manual and having some
trouble explaining why score and book blocks are introduced
with \score and \book commands rather than \new Score and
\new Book commands.

Since it is possible to have several score and book blocks
in a single input file, the user might intuitively expect
these to be introduced with \new Score and \new Book in an
analogous way to \new Staff or \new Voice.

Is this simply due to the way LilyPond developed
historically or is there some deeper reason?

Trevor D