Idea has been to keep this monthly.
Originally idea was that you had 1 month to submit, and then the during next month people would keep playtesting and sending feedback.
Then by having monthly, you can keep submitting your game continously, at any time, and also get constant feedback.
If there would be running only one at a time, as in, one every two months, then that would mean you could submit your game only every second month, and similarly get feedback only every second month. This way you will always be able to submit your game, and also always be able to get feedback.
Also, as so far there seem to have been enough interest that people have been submitting their games, I have been holding a new one every month. If interest drops, then I will start holding these less often.