Why does Pages force me to waste the last line in the page?
This occurs because of a pagination option called "Prevent widow &amp; orphan lines". By default, Pages prevents the first or last line of a paragraph from appearing on the bottom or top of a page and separating it from the rest of the paragraph. These lines are called widows and orphans.

To disable this, select the text. Then, under the Format sidebar on the right side of the window, click the More tab and uncheck "Prevent widow &amp; orphan lines."