The easy answer is that they are all piloted by Bigfoot who is himself surrounded by a blurry cloud like Pigpen in Charlie Brown land thus blurring everything in his vicinity.
The hard but most correct answer is that though many people routinely carry devices with cameras with them everywhere they go, when an event like many described occurs it takes time for someone to get the device into camera mode, focus the camera onto an object or event that could be in motion towards or away from them creating significant issues for the sensors in tracking and focusing past things like window screens, leaves on trees in the foreground, infrastructure in the near field hampering focusing on smaller objects in the farfield, etc.
I have a device that I carry with me that purportedly has a great camera. Yet, in spite of the technological marvel that I have in my pocket, I have on many occasions attempted to take photos of simple everyday objects like birds migrating over my property, insects in my garden, etc that should be easy. Instead I have an impressive collection of out-of-focused photos because it turns out that even with the best sensors and excellent optics it is not trivial to get the sensor to understand which element in the field of view it is supposed to focus on without making some effort to assist it.
I am willing to wager that most people who have these devices, like myself, are not trained photographers and that this fact explains why most photos are poorly focused and have no cultural data that allows one to estimate size or other physical characteristics.
I photograph air shows when they have them at the nearby airbase because planes are cool and I grew up near a large military installation where the air was filled with the sounds of helicopters, jets, and artillery practice way back when the Vietnam War was still a thing. As a kid it was cool to see all this and as an adult it is still cool. The last time the Blue Angels came to town I took hundreds of photos using an fairly ordinary digital camera with lots of megapixels and great digital zoom that works well for shots that are easy to compose. Of the photos that I took from a vantage point less than half a mile horizontally and with the jets passing a few hundred above the terrain I ended up with a handful that are truly well focused and worth showing off. I blame the photographer, not the camera. I also suspect that most of the other people in the crowd that day also have a similar uncomfortably large collection of slightly out of focus photos of objects flying past them on a clear, cloudless day.
To me, the absence of clear photos of any of this is explained by the context that the photographer was operating in at the moment - attempting to take a photo of something they considered strange, exciting, or extraordinary while keeping it in the field of view of the camera, adjusting focus and zoom, etc.
My own bias, since we all have biases or we would not offer and defend opinions so freely, many times with very little supporting evidence, is to believe that something has been happening globally for a long time that is worth studying so that we can all understand why it is happening. I will keep the popcorn popping and enjoy reading any updates or debates and if I get lucky to live long enough to see a clear photo and a definite answer then I will consider that bucket list item crossed out.