A lot of that is because Google doesn't define success that way. Their view is that anything that stimulates the internet will indirectly benefit them, so that makes products like gmail or chrome clear winners. Gmail brought us threaded emailing, ajax (and good javascript-supported interfaces in general), etc. Chrome brought us tear off tabs, fast javascript execution, etc. I think if the focus was stand alone profit generators the products they put out would be very different - what would Android look like?

*brought us = made popular, not necessarily invented.