'Dancing With the Stars': Why is this the lowest-rated season?

While the media has focused on the fight between NBC’s The Voice and Fox’s The X Factor, another performance competition series has been setting records of its own — and not in a good way.

ABC’s Dancing With the Stars tied its all-time ratings low Monday night for a performance episode, down 9 percent from last week. The show delivered 13.4 million viewers and a 2.1 in the adult demo. Gee, that still sounds like a lot of people watching, you think. And you’re right. In fact, Dancing was Monday’s most-watched show. But that’s still a much smaller audience than the veteran series used to deliver and that modest adult demo rating is the real concern. Overall, this is the show’s lowest-rated season.

Maybe it’s the All-Stars format. Maybe fans wanted new faces. But Dancing has been on a steady downward trend in recent years (surely one of the reasons the All-Stars format was attempted in the first place). And as we’ve seen with American Idol and Biggest Loser and other shows, once a reality hit is on the far side of its ratings bell curve, it’s tough to reverse the trend. With these numbers, Dancing isn’t going away anytime soon, but its starting to look mortal.

Dancing led into Castle (10.1 million, 1.9), down 14 percent to tie its all-time low.

Also of interest Monday: Fox’s The Mob Doctor (3.9 million, 1.0) returned! What, you didn’t see all the tweets and parades? The struggling drama actually did rise a tenth of a point from its last telecast. Its Bones (5.4 million, 2.0) lead-in was steady.

NBC’s The Voice (12.2 million, 4.5) was down 6 percent and Revolution (10.7 million, 2.9) was down a tenth.

CBS also had its comedy block, with new comedy Partners (5.8 million, 2.1) flat and the rest of the lineup dipping slightly. Partners has a number that would get a pickup on another network, but CBS treats stragglers in its Monday block like the owner of a bar at closing time: You don’t have to go home but you can’t stay here. CBS also aired HIMYM (7.2 million, 2.8), 2 Broke Girls (9.1 million, 3.3), Mike & Molly (8.8 million, 2.8) and H50 (7.3 million, 2.0).

The CW had 90210 (894,000, 0.4) and Gossip Girl (654,000, 0.3). Ugh.