HOW DID VEGETARIAN DINOSAURS GET SO BIG AND STRONG?

I swear I'm gonna just keep recycling these three images until long after everybody's sick of them. But only a meat-addled brain would not understand that the earth's largest and most powerful land mammals tend to be entirely vegetarian. So is it really so freakin' inconceivable that enormous sauropods would have been well-nourished by an entirely plant-based diet? Still, as long as people think this is news, I'll certainly go ahead and help spread the word.