#4 Not adding more matches onto the card

I don't recall any other time when WWE had only four matches confirmed for a PPV that was scheduled to take place in a few hours. If you do, be sure to let me know in the comments below.
Many fans complain that WWE's PPVs are too long and tedious and they're filled with meaningless matches, but that still doesn't explain why WWE decided to have only four matches for Hell in a Cell.
Having four matches in an event as big as this one means that there will be a lot of unhappy Superstars. There are so many champions on the main roster right now, and for them to sit out a PPV for no apparent reason, it won't sit well with them. AJ Styles, for example, the current United States Champion and one of the biggest Superstars on the roster, won't defend his title at Hell in a Cell after competing in the pre-show for Clash of Champions.
It's not too late for WWE to add another match or two to fill out the card. They're notorious for doing things at the last minute, so this will not be their first time. Shinsuke Nakamura could defend his Intercontinental Championship against Ali while Roode and Ziggler could defend their RAW Tag Team Championships against The Viking Raiders.