There are many things the WWE creative team does that fans don't generally agree with, and Cesaro being held back from the main event push is one of them. The Swiss Superman is one of the most talented in-ring performers in the world, and has seemingly gotten over with the crowd.
Though Cesaro hasn't been given the singles push we've all been waiting for, he and Sheamus have flourished as a duo, and currently, hold the Raw Tag Team Championships. But those following are aware that the Celtic Warrior is dealing with spinal stenosis, and the WWE is being careful with how they use him in matches.
According to Justin Barrasso of Sports Illustrated, Cesaro's singles push is being delayed because WWE wants him to stick with Sheamus and protect his partner. By doing this, Sheamus' career can hopefully last longer. Without Cesaro, there wouldn't be much he could do in singles competition. Barrasso also believes the upcoming Royal Rumble is an opportune time to break up the tag team.
If (and eventually when), The Bar disbands, you have to wonder what the future holds for Sheamus. It should be noted that his injury is what ended the careers of Hall of Famers, Edge and 'Stone Cold' Steve Austin.
Nonetheless, the Swiss Superman has succeeded as a mid-card performer. He's won four Tag Team Championships, one United States title and the 2014 Andre the Giant Memorial Trophy. Wrestling Observer Newsletter also named him the Most Underrated superstar every year from 2013-16.
It remains to be seen if Cesaro will really get that big push in the new year. But at least we finally know why it's been put on hold over the past few months.