Because it could be really, really cool. As an engineer I like "hard" problems, and when I find a project interesting I go after it -- regardless of how "flashy" it is to the general public.
I think in Google's case, this is certainly true if you examine how much work has gone into their infrastructure (and how many research papers have been written on those topics).
A successful [software] tool is one that was used to do something undreamed of by its author. -- S. C. Johnson