They're filling out the grid. There are 31 brands (if I counted correctly) which doesn't fill out any grid other than 1x31 or 31x1. They filled it out to 40 because that gives a nice grid at the larger size (4x10) and smaller windows (2x20) while not leaving any empty spaces.

If they kept it with 31 there'd be empty space at any reasonable column count (2, 3, 4, 5, 6). Past 4-6 columns it starts getting too busy across the screen (subjective). They seem to have capped it at 4, it drops to 2 and then 1 as you narrow the page.

One filler image works at each of those sizes, but then it's odd to have a single filler image. Pushing it to 9 gives a ratio approaching 3:1 brand:filler images, someone looked at that and said "That looks better". The filler images are placed, it appears, next to their associated brand (the cupcakes and Sara Lee, as an example).

Whatever the 7th row, 4th column is, it does not look appetizing.