Creating communities is hard, but Google wants a unified 'Google' community, not multiple disparate ones -- just look at how they handled YouTube.

Even if you throw in some machine learning to figure out if the user's looking at memes or gifs or porn, I can't imagine the marginal value of that data being of use to Google. It's essentially unmonetizable, which is why most image hosts disappear after a few years.

Imgur was successful in avoiding that fate by pivoting to a community, but that community would be of no use to someone like Google.