Sprites' drawcall can't be batched when using perspective camara

Hello everyone
I'm developing a 2D game with multiple layers of parallax, like Tails of Iron How, so I'm using the perspective camera.
After the art set up the scene, I found that the scene built by ten textures actually has more than 100 Drawcalls. After I Google it, I packaged their textures into an atlas, sorted the layers, layer order, and z-axis all set to the same, but it still has more than 80 Drawcalls.
Finally I tried to change the camera to orthogonal camera and the drawcall came down, please tell me why?

 

They both use the material Sprite-Lite-Default and have exactly the same settings on SpriteRenderer.

 

Have you tried running it with the frame debugger and seeing what happens differently with perspective vs ortho?

https://docs.unity3d.com/Manual/FrameDebugger.html

 

perspective :


ortho: