Your strategy is too risky for investors' appetite, that's my guess. Your strategy has a maximum 43.5% drawdown which means an investor can lose close to half of his/her money and your win ratio is less than 50% so your strategy is losing money more than half of the time. And the bulk of your winning is concentrated in this one month of December. This is a kinda of a swing-for-the-fences kind of strategy. For more than half of the time, you don't win but this one few times that you do win, you win a windfall. But during the time that you are losing, you could lose almost half of the invested capital. So after losing almost all of the invested capital, how does an investor still have money to invest to win the windfall?
This is what goes on in an investor's mind when he/she is looking at your strategy and this is probably what the algorithm takes into account when assessing a strategy's eligibility to be included on the leaderboard. So if I were you and I wanted to improve my C2 score, I would tweek the strategy a bit to lower the max drawdown and increase the chance of winning a bit. I mean think about it, if you were to invest your own money, would you invest in a strategy that only wins less than half of the time and can make you lose almost half of your money? If you would, then f the Collective2 and just trade your strategy with your own money. You would make 242% return on your invested capital, that's more than double the invested capital, who gives a s about subscription fees? You will be richer than Warren Buffett in no time.