As Metlzer has said, when you overuse "extreme" eventually you wind up in a place where there is no place to go. Dumb comparison, but if everybody says the F word every five minutes, the word loses its meaning and effectiveness. But if a straight laced preacher or something gets so made he says the F word once every 3 years....then it is like space and time stop because everyone is so stunned. It now MEANS something.
So what does that have to do with wrestling? One Hell in a Cell match every 2 years.....in a feud that MEANS SOMETHING.........and NOT doing anything resembling it for 2 years means when you finally let that cat outta the bag...it MEANS SOMETHING.
When you have the right feud with the right people and it is going well, you will no when it it is time to put those two in a cell. But randomly throwing it up is like having brithday cake for breakfast everyday.....big deal.