Like-minded drivers have caught amazing videos of meteors. Planes could do the same for supposedly legitimate UAP sightings.
https://www.cnn.com/2019/04/30/politics/boeing-sensor-737-ma...
I'm guessing the reason they didn't put a lifesaving backup sensor on the plane might be sorta similar to the reason they don't add high-definition cameras in case of UFOs.
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.