Speaking of satellites, aren’t there cameras up there watching everything...all the time?
No, and here is why. To begin with, a large percentage of Earth's atmosphere is full of clouds. Perhaps airplanes spend most of their flying time above clouds... but most crashes occur below them. Then satellites don't see anything at night.
But that's far from being the only reasons. The primary reason is that Earth is BIG. Surface of Earth is 510,072,000 km2. Let's say you want to resolve an airplane (100 m long) as one pixel. Not much good will it do to you, but we'll start there. One square kilometer will then require 100 pixels; the total pixel count will be 51,007,200,000 - or 51 BILLION pixels. That is per frame; but, of course, you want more than one frame. Let's say you are willing to settle on one frame per second. With each pixel requiring 3 bytes (RGB888) we then need just a trifle amount of 11.743 PETAbytes per day. Wirelessly, from the orbit.
Even if you go for this huge expense of filling the sky with satellites and equipping them with that much RF bandwidth, all that it buys you is a single gray pixel per aircraft, once per second. This is useless for just about anything. You cannot judge anything by a single pixel. If you want more resolution then you need data links and processing capabilities not of this world. Just 10 pixels per aircraft will increase the bandwidth by a hundred, and then it becomes 1100 petabytes per day. This is more than all the Internet traffic (wired, in fiber!)
But, you may ask, why do the spy satellites work? They work simply because they do not look everywhere. Most of the Earth is a boring place; nothing ever happens there. Spy satellites have telescopes; they may be able to read a license plate on a car; but they are not able to read it here and in 10 miles away, and at a time of your choosing. Their view area is limited by magnification of the telescope. The higher is the zoom, the smaller area they see. And that's why the zoom ring on a telescopic sight is the most valuable control - you can't see the area while zoomed in, and you can't see the target in detail when zoomed out. Go to a football game with a good Orion telescope. You will be able to see every blade of grass in the farthest corner... but you won't see the game.