Every time you scroll 20+ CPU cores have to hum away and generate previews of websites (assuming they aren't cached already). So it's mostly a server load optimization.

And on this note, I use the Vimium browser extension (vim-like keybindings for a lot of things) and scrolling all the way to the bottom doesn't cause more results to appear.

I do expect some breakage when using a niche extension like this, but it seems like it would be fixed for my use case if something like plainOldText's idea were implemented.

edit: Or if the scroll button thing were an a tag, I suppose I could "click" it like any other link from the keyboard. It does load more (somewhat reluctantly) if I scroll down with the arrow keys.