Madam Speaker, it is because that is not what the motion says. The motion calls on the House to mandate the government to initiate the process. It is as simple as that. Deciding what form this will take will come later.
I know that the very idea of a republic is a bit foreign to a Canadian government that is proud of its monarchy, that it is a rather alien concept that may be hard to understand. There is also the idea of consulting the public, deferring to the sovereignty of the people, where the people get to write their own Constitution, make their own choices and decide which institutions they want.
However, I guess that can be hard for a descendant of British colonialism to understand.