It's because the PDF is generated from HTML, and the table expands to take up the width of whatever container you give it, whether that's a portrait container or a landscape container.
Landscape just makes a wider table, with no more or less whitespace than portrait or than a billboard (proportionally, that is).
If the goal is to write line-item level notes in the table, then a "SKU Notes" column can be added and Landscape gives it more horizontal space to exist.
But the first step is to confirm that this is indeed the objective because "just make it landscape" wouldn't achieve anything on its own.
Landscape just makes a wider table, with no more or less whitespace than portrait or than a billboard (proportionally, that is).
If the goal is to write line-item level notes in the table, then a "SKU Notes" column can be added and Landscape gives it more horizontal space to exist.
But the first step is to confirm that this is indeed the objective because "just make it landscape" wouldn't achieve anything on its own.