In my opinion, it is just a time of quietness on Synfig community. Some of the people who entered in the previous challenges are busy with other stuff (included me). I think that the Synfig’s mascot is a great challenge to re-pick later, when the Synfig’s community excitation were higher so we can obtain great entries.
Maybe, to invite participation, it is better to propose the challenge with an entry. This would imply more work to the challenger because he would have done the challenge before propose. In this way, just pick up an old challenge and submit an entry would provoke someone to participate.
Possibly, monthly, implies some sort of obligation, and it is not funny at all… because this is just for fun, right?