Hyunho Shin,
MIPI-CSI2 can receive frames up to 8192 x 4096 pixels, but if you need to process the image on some other IPU block (e.g. rotation, resize and etc), the frame size will be limited.
For example, if you need to resize or rotate the image, it will need to pass through the image converter (IC) block and it will limit the input image to 4096x4096 and the output image to 1024x1024. See reference manual chapter 36.3.1.5.3 Image Converter (IC)
This should be the reason you have this limit.
Rgds
Rogerio Pimentel