The WWE doesn't know how to make tag teams relevent or credible without them holding the tag team championships. It seems as though when a tag team challenges and fails to win gold, they fade to obscurity to the point their reputation suffers permanent damage. I think one of the main reasons for this is the lack of tag team feuds that don't involve the belt. If you had established tag teams battling each other frequentlyr, it would keep them relevent. Legacy vs. Dx is a great example of this, Legacy really set themself up as a tag team to watch out for as a result of that feud, they didn't need the belt.
I believe the reason there aren't more tag team feuds is because...(you guessed it) there aren't enough tag teams. The only other tag team that the Usos can really feud with now is Marella and Kozlov, at least people still know who they are...i mean, who else can they feud with? Sure, they're being made to look like jobbers now (well, that's all they ever were really) but if they did beat Marella and Kozlov, they'd have no where to go after...at least Marella and Kozlov are getting a good reaction by winning.
What i would personally like to see is the Usos feuding with R Tuth and Morrison, maybe working for Ted...it would definately keep the relevent. But that stroyline is too complicated for the WWE midcard, and other than generating interest among those especially interesting in the Usos or midcard, it's not worth the effort.