This is because the so-called ‘UFO’s and the site Area 51 containing evidence, is just cover for various military projects.
For example, the TR3B.
Many of the UFOs are cover for military projects.
Many are not.
Here is an interesting podcast discussing those that are not:
https://podbay.fm/p/aliens-and-artists/e/1645119331
Everyone thinks is that the F-35 is the absolute best that we have….😂😂😂😂
UFOs have been seen long before Area 51.