There is no definitive reason on why networks turn down or accept videos. Some advice to help your chances at getting picked up are as follows...
1. Have a good production look to your video. Make your video as visually pleasing as possible. Videos that look like they were shot on a cell phone or having a low production value will decrease your chances at getting picked up.
2. Limit sexual/explicit content from your videos. The networks use Standards & Practices when reviewing videos. Although videos can still be accepted with explicit content, they would require edits in order to be played. It is better to submit the video as clean as possible. We have noticed tendencies that the cleaner a video is the better chance you have at getting picked up.
3. We recommend checking our clients section before shooting your video. You can see videos on there that have been picked up by the networks, and it will give you an idea of what they are looking for. You can then have a better understanding when shooting your video.