You must just be missing them when they come up. I just took a look and the 30th Thematic tourney started on February 1st. The last knockout started January 1st, and the last regular started December 1st, 2015.
Next regular should start on March 1st. I don't know when they actually get posted.
I believe they alternate between normal tourneys, quick knockouts, and thematic ones each month.
The Chess.com official ratings-split tournaments used to come around every 3 months, but seem to have trailed off recently; any chance of a new round soon?
I certainly enjoyed them, and sure many other did as well given the amount of players who signed up!