Facebook and Instagram do a significant amount of automated filtering. People from scammers to spammers to pimps have incentives to try to bypass the filtering. It's a cat and mouse game Meta has a significant incentive to stay ahead in; everyone from advertisers to app store owners to users will punish them for having too much of any of that, or even legal adult content.
Policing is the job of the police. If criminals are advertising sex with children on Instagram to the point that child molesters can find it, police can find it too. They can then use the low-tech method of posing as buyers, witnessing illegal acts, and arresting the offenders.
Instagram should provide assistance when legally required and technically possible of course, but should not be expected to perform law enforcement functions. That's not just because it would be some sort of undue burden on the huge corporation operating it, but because it lacks the checks and balances we apply to police agencies.
Policing is the job of the police. If criminals are advertising sex with children on Instagram to the point that child molesters can find it, police can find it too. They can then use the low-tech method of posing as buyers, witnessing illegal acts, and arresting the offenders.
Instagram should provide assistance when legally required and technically possible of course, but should not be expected to perform law enforcement functions. That's not just because it would be some sort of undue burden on the huge corporation operating it, but because it lacks the checks and balances we apply to police agencies.