another question regarding ottava: why does Lilypond change the pitches?

[Kenneth Wolcott]

Hi again;

another question regarding ottava: why does Lilypond change the pitches?

If the purpose of the ottava is to make it easier for the
publisher/engraver/typesetter/performer to read the notes within the
staff rather than lots of ledger lines above or below the staff, then
why does Lilypond display the changed pitches AND display the ottava
brackets?

Thanks,
Ken Wolcott