Wishful thinking, I know.

With the progress of technology, it really is difficult these days to grasp what the military is capable of. We keep breaking grounds of what we previously considered possible. Though there have been reports for decades of object maneuvering that we still haven't publicly replicated or properly explained. Assuming any of those reports to be true, that either suggests there is an external factor, such as NHI, or the government has been concealing groundbreaking technology for way too long.

Some plausible scenarios I've come across that tie in with your second point are...

• The government has documented UAP this whole time, but doesn't have a comfortable grasp on what it is. Revealing that could be seen as a vulnerability, so they'd rather dismiss it than appear weak to the nation and world.
• They've recovered technology of NHI or unknown origin and have been reverse engineering it for decades. The silence on it would then be to keep the advancements between the DOD and private contractors to benefit from. And/or, to cover potential illegal activity in the acquisition and monopoly of the technology.

There are a lot more scenarios I've seen, but these seem the most plausible and accessible.