It’s not so much a decline in discussion, more a decline in claimed sightings or reports. Used to be that someone would see something weird, something they couldn’t explain them selves, and then they’d go tell people about it, but their story would be patchy, low on details, and eventually someone would be like “must have been aliens!” when no one else had a good explanation.

But now people just take a high resolution video with a phone, they post it online, and someone who recognizes what’s going on immediately explains it, thus it doesn’t get noted as a UFO/UAP because it has been identified.

Thus there is a lot less “unidentified” things for people to default to assuming are aliens. Notably a lot of the things people like to point to these days are videos from thermal cameras taken at super long distances with details are poorly resolved, thus making it harder to “identify”.