Why do most FPV 5.8 GHz video transmitters use PAL or NTSC?
As others have said, PAL and NTSC are analog and have virtually no latency. This is extremely important when flying FPV drones at high speeds. Having latency will tell you where you’ve been, not where you actually are.

I have a large video/photography drone (Yuneec Q500 4K). It transmits the video digitally on 5.8&nbsp;GHz using the 802.11A protocol. (Just like your home Wi-Fi network.) I have measured the latency of the video feed at 282 milliseconds. This is because the video has to be converted from analog to digital, and then the back again at the receiver. That may not sound like a lot, but it is when you are traveling at high speed and trying to avoid obstacles.

Here is a quick chart that will show how 282&nbsp;ms of latency affects where you think you are, compared to where you actually are.

Speed    Error       Speed     Error
[MPH]    [Feet]      [km/h]    [Meters]
----------------------------------------------
 10      4.15         16       1.26

 20      8.24         32       2.51

 30     12.39         48       3.78

 40     16.54         64       5.04

 50     20.63’        80       6.29


Considering that some FPV drones can travel at 60+ MPH, you can see how much of an impact that video latency would have.

As far as FPS goes, 30 for NTSC and 24 for PAL are standard frame rates and more than enough for a smooth picture. Higher resolution would also require larger/heavier hardware. When FPV racers are trying to shave fractions of a gram off of their drones, they will sacrifice resolution for a reduction in weight.

I hope my explanation helps!