It's hard to be a tag team, especially in WWE where their amount of star power is just through the roof at the moment. They have to get all their big stars on their shows and that leaves very little time for tag team action, but as far as creating new teams, I think they're moving in the right direction. The Usos are still stable, Epico and Primo have been on a roll, if Camacho ever becomes an active superstar we could see him begin to team with Hunico, PLUS we have semi-tag teams in the form of Swaggler and Truth/Kofi (although on a personal note, I'd hate to see Truth and Kofi come together full time). I sure I'm already overlooking some of them, but the fact of the matter is, there are some there, and some on the horizon.
Luckily, WWE is getting their new network, which calls for more programming, and hopefully since they'll begin to have more opportunities to diversify their megastars' appearances, allowing more time for tag teams to get rolling and have a little bit of the spotlight. I don't know if that's something I'm really holding my breath for, but it could happen.
And in TNA, I can't really complain about their tag division. You've got an awesome set of tag champs in Magnus and Samoa Joe, you've got Mexican America (who, really, aren't spectacular), Ink Inc, EY and ODB (maybe?), Crimson and Morgan (also maybe), and as soon as Sabin gets back to proper condition, we'll have MCMG back in action. Plus, the members of Immortal could team on any given night, which allows for combinations like Gunner and Steiner, Steiner and Roode, Roode and Bully, Bully and Steiner, Bully and Gunner, Gunner and Roode and anyone else. I think TNA's pretty stable, so I wouldn't call it a lost art in all major promotions.
And depending on how you label ROH, they could be considered a major wrestling promotion, and I don't even need to explain why their tag division is awesome. If you need an appropriate reason, I've got only two words... BRISCOE, BROTHERS...
But yeah, no one is really going to argue that tag wrestling was at it's best a decade ago and the decades before. I sort of blame it on the fact that gimmicks have also become less diverse, and because of that, you know longer have two guys brought together under a singular gimmick. Like Samu (or Sionne) and Fatu as The Headshrinkers, both being savage samoans, or Demolition, LOD, or The Power of Pains all being face painted monters hellbent on destruction. Then you had the rock 'n' roller teams like the RnR Express, The Midnight Rockers, or the Rock 'n' Roll RPMs for that matter. What I'm getting at is that when bookers were more interested in developing dynamic gimmicks, you saw more guys pulled together to play the part. Now that wrestling is less gimmicky and not everyone has their own persona entirely unique from the others, you don't see guys united like they used to be.