It's unreasonable because installing and maintaining aviation qualified cameras is expensive. You can't just strap a consumer action camera to the wing and expect the FAA to approve. Airlines have no incentive to pay for extra cameras.
Just because things are as they are, doesn't mean that they couldn't be better.
But regulators do revisit existing rules all the time. If you really want this then feel free to file a formal petition for rulemaking. If you do that then they'll have to at least look at it.
https://www.faa.gov/regulations_policies/rulemaking/petition
It would be pointless for this use case anyway. The field of view through the cockpit windows is very narrow and any UAP would only show up as a few blurry pixels.