I've seen zero evidence that Pinterest can actually generate a profit. They do not make money from every product someone pins, and there's no reason to think they ever will. The only thing I've seen so far is speculation and theoretical future business models that may or may not pan out.

Github however is profitable and has a proven, functional business model. Github is absolutely not fighting a losing game, because they're providing a service companies obviously desperately want to outsource (thus the mass usage). Providing that service in a secure manner is worth a lot of money, as Github is protecting something extraordinarily valuable.