mp_productlist.php not listing all products

I am building a custom theme and am trying to show all products on a single page (there are only a few).

If I leave page.php alone, it shows all the products no problem.

Then, I try to save page.php as mp_productlist.php and upload that, expecting to get the same results as page.php. However the styles are all different (somewhat expected) and, more importantly, it only lists 1 product.

Why is mp_productlist.php no longer showing all the products, and how can I make it do so?