I'd say because it's more delicious, but that's not what Brian Wansink of Cornell University Food and Brand Lab found out: it's because meat is macho.
"To the strong, traditional, macho, bicep-flexing, all-American male, red meat is a strong, traditional, macho, bicep-flexing, all-American food," write the researchers. [...]
If meat represents masculinity, it would seem men would be more likely than women to prefer meat to other foods — a means of reinforcing gender. To test this idea, the researchers analyzed data of more than 2,000 university students who indicated how much they liked or disliked various foods. Male students were significantly more likely than female students to like beef, meat and orange juice; and the women were significantly more likely than guys to like salad and vegetables.
This "masculine meat" phenomenon seems to hold in other countries as well. In one study of 23 languages with gendered pronouns, the researchers found "that the vast majority of these gendered words and these languages associate meat with the masculine pronoun," Wansink told LiveScience.