To serve you the 5 millionth search result for "funny"? Unless you are going to directly pay for that server cost it just doesn't make sense, and it is such a rare use case that it doesn't even make sense for them to give you that option. They have to cut you off somewhere. When is the last time you legitimately wanted the 401th page of the search results? It will be more efficent for both you and Google if you instead refine your search query than paging through the results forever.
They have literally one job.