Using saliva is permitted though. Most of the players used saliva, but was busy chewing gum or something else and that was the cause for the fines. Every team has a designated person that shines the ball for them to try and get as much as possible out of the ball for them within the rules of the game. Sure these guys overstepped in using other things such as gum or something else, whether it was on purpose or not, but you can't put them in the same bracket as the sandpaper trio.
Reason being:
1. There was a deliberate scheme by the Captain, vice-captain and the culprit (Bancroft) to conspire and do what they did with them knowing that it's beyond the scope and boundaries of the ICC Rules and Regulations.
2. They did it in such a manner that they wanted to hide what they are doing, and had they not been caught on camera, they would have gotten away with it.
3. Their team-mates, well most of them, didn't know what they were up to, neither did their administrators and selectors.
4. The fact the CA went to such a length after the incident, made it clear that it was a much bigger issue than the other incidents.
To make the ball rough on one side is a tough thing to do, and their plan was to get it to reverse, something their opposition wasn't able to do in that test either, they failed with the bat and tried to save face with the ball. It was a very tough series, and they got their asses handed to them.
They were so consumed with winning at all cost, that they felt that cheating would be okay, even if they get caught.
Now cooky, in the criminal justice system, we would call that Premeditation. And that usually warrants the most extreme penalties.