Why are we eating beef but not Turkey?

We are in Istanbul, Turkey today. I want to celebrate this by eating everything in sight. Sadly, that's not going to happen. I ate a lahmacun, so in understandable text, a turkish pizza. To eat this pizza you receive a pizza crust, that looks like a quesadilla, with beef in it. B-b-beef in it, not turkey, beef! Then you put salad and fresh squeezed lemon inside of the pizza. Finally you roll it up and eat it! I don't get it, but I loved it.