Most of these weren't things pilots saw with their physical eyes. You need to pay attention to the accounts. There are some though, to be clear. But these cases aren't like the ones we're seeing videos of. They are often something that flew between the aircraft vertically. This could easily be a bird (lower altitudes) or even part of a weather balloon that is just in free fall (these are launched all the time and have small payloads that frequently fall into the ocean). There are also tons of surveillance drones (foreign and domestic) and a few of these have been seen at night and when people look through night vision optics they'll see triangular shapes. This is something you can replicate, which builds strong evidence.

I don't know if you've ever been in a small private aircraft, but if you have you may have seen another plane crossing your path. It is quite hard to see such an object until it is right on you (thank god for ADS-B). I couldn't imagine the same situation in a fighter jet. Having also seen things like balloons and birds while flying, I can tell you that things don't look the same. Your perspective is really different and optical illusions are abound (people even frequently misinterpret flight paths looking up at planes and birds). Yes, you get training for this, but at the same time that training doesn't break the illusion.