[pjreddie]

NIPS is more math/theory heavy as a conference while ICCV/CVPR/other vision conferences will tolerate less math and more pictures. You have probably been reading mostly vision papers but if you read more papers targeted at NIPS you will find more math. This looks to be an ICCV submission, whereas if you read the original GAN paper (a NIPS paper) there are theorems and proofs. Your observation is correct, you are just comparing different subsets of the field.