Why did flatbread dominate the Middle East but Europe adopted raised breads?
I'm going to agree with Szczerzo about this being an anthropologic question, but I'm going to disagree about the cause.  While nomadic lifestyles was an influence, it's not causative.

I'm also going to ignore the distinction made about raising agents in the OP, because it's factually incorrect; most Arab/Levantine/Turkish/Kurdish breads use yeast.  Instead, I'm going to answer the distinction between loaf bread and flatbread.

Specifically: loaf bread is an aberration, not flatbread.  You find flatbreads around the world in every society that has access to any kind of grain anywhere.  Europe, Asia, Africa, Americas, Malaysia, everywhere.  Some are raised (yeasted) and some are not.  Some are filled and some are not.  All grains are used: wheat, barley, millet, rice, lentils, corn, etc.

Whereas: loaf bread pretty much only shows up in Egypt (and nearby) and in Europe, and there's good reason to believe that the latter two regions learned it from Egypt.  Thing is, loaf bread requires several different things to be easily and cheaply available in the same place:


Wheat or barley (high-gluten flours)
Ability to build brick, stone, or earthen ovens (this is where nomadism isn't compatible)
Ability to cultivate starters (both the right grains and the right weather)
Inexpensive, but hot, fuel for ovens (e.g. wood)


This combination simply didn't happen in too many places; either people lacked suitable grains, lacked cheap fuel, didn't build ovens, or simply never got started (the Babylonians appear to only have made flatbread, for example, despite having all the right ingredients and tools).

So it's really not so much a question of "why did X culture only make flatbread" as "why did these three places make loaf bread?"

If you're interested in this, I highly recommend the book Six Thousand Years Of Bread.