#4 Lack of challengers on both WWE brands
The depth of the tag team divisions on both WWE RAW and SmackDown isn't great. There are around 3-4 viable challengers on either show, but most of them have a member who is unavailable at the moment, while WWE's recent release of the Authors of Pain, who could have been the next RAW tag team champions, hasn't helped matters.
The Red brand's tag team scene does have some life, with the expansion of The Hurt Business. But the tag team division on SmackDown is lifeless. Cesaro and Shinsuke Nakamura don't have anybody to face beyond Lucha House Party, unless Heavy Machinery decides to challenge for the titles, despite Otis being Mr. Money in the Bank.
Both tag team divisions run the risk of having repetitive feuds just to fill time, and as a result, there is hardly any steam in any of the top feuds for the titles. The Street Profits' 6-month reign as RAW tag team champions has not been the most memorable because of this very reason.
Things would be much simpler, and better stories could be told by WWE if there are multiple threats to the tag team champions. Right now, there is barely one each for the current RAW and SmackDown tag team champions.