I think there are many more alternative reasons.
For starters you have not addressed the issue of major corporations making a lot of money from alien technology.
Then we have the issue of governments conducting criminal acts to keep secrets—which forces them to keep doing more criminal acts to keep those secrets—in an endless coverup loop.
I also think there were patently illegal and unconstitutional (not to mention immoral) treaties between human governments and aliens.
Then we have the deeper problem of “fake history”—layers and layers of fake history. Those historical narratives are what persuade folks to be loyal to their government—and when ripped away the populace may become outright hostile.
There are more reasons as well.
This rabbit hole is very very deep.
I would put the major corporations benefitting as the first and fourth option.
Can you imagine the outcry if the technology would eliminate the vast use of oil? Or provide “free energy” to desalinate water? Or eliminate the constraints of shipping/transporting stuff from one point the other?
The people of the world would be outraged, in the literal meaning of the word.
I think the lies are so deep that no one wants to step up and say, “Guess what…”
Unless one of those ships lands on the 50 yard line of the World Cup or Super Bowl…”Governments” will never reveal what they know. There is ZERO upside and a whole lot of downside. So…they just keep lying to our faces.
No files, no photos, no evidence, no non-human materials? No problem.
Why the concern over a bill demanding the release of such things if they don't exist?