Istanbul is massively massively spread out, and because of that loses many of the economic benefits that non traditional cities have. You really can't have your cake and eat it too here...
Istanbul has some problems that has forced it to spread around... Being in between two seas with the Bosporus strait in the middle takes a lot of directions for growth away. And most of the "traditional city" areas are so full of archeological sites that you can't really build much there.
Those areas are quite lovely to live in, though. I really enjoyed Besiktas and Beyoglu back when I lived there
Istanbul is 2nd largest city in Europe and they still have a huge traditional city core and outskirts are pretty close too. They have some subway and rail and ferries. I can't say I fully understand how they manage without collapsing, tho.