Doing the math:
Cost: 60% of world's agricultural land
Benefit: 5% of protein and 2% of calories
Normally, when a food item is really expensive, we eat it rarely and call it a delicacy. Trouble is, the expense of tying up that much agricultural land (significant contributions to world-wide hunger and global warming) isn't borne by the consumers of beef, so we in the "developed" world think it's much cheaper than it really is, and eat it all the time.