Actually Facebook is not "cat pictures." It's a very efficient advertising engine the same way Google is. Similarly to Google (whose revenue is dominated by search ads), Facebook has feeds straight to consumers as well as valuable information about what the consumers are interested in. That's what makes money. Instagram, News Feed, Facebook News --> these are Facebook's Google Search & YouTube.

When you look at the numbers you'll see that they're actually similar companies who've monopolized segments of the digital advertising space. If you're going to complain about Facebook's market cap then you should also complain about Google.

Facebook's even got "other bets" -- Oculus, Workplace, WhatsApp, etc.