The thing is that, selfie verification was introduced and implemented into the kyc system by majorly every centralized company that runs on the internet, so this is not something that is peculiar to gambling casinos alone, even cryptocurrency exchange platform does require selfie or video verification and I dont think it can be bypassed, except like you said, the user decides to use a fake document, and in the stage of selfie/video verification is where the real challenge will begin, except on occasion where the owner of the documents being used is a close fiend or relative, then the person can try and convince he whose document is being used, to pose to the camera for the selfie or video verification.
The need for selfies arise due to the many issues of identity thefts that have graced many of the online casinos kycs, since hackers have access to some stolen documents that their used to verify fake accounts in those users name and identity just to. Exploit the casino then the casino came up with selfie so as to very the facial and the real time identity for the users that want to very accounts instead relying on mere document submission and this have really helped casino to combat the issues of fake identity verifications.