Successful percentage is rare when it comes to new projects inventment. Even you have know idea how many projects getting launch daily! So so it'll be so difficult to decide where to invest, which one should pick up. And result will be negative in most of the cases. But it's true that new projects also getting investors otherwise failed to get successful but not everyone have extra money for experiment and taking risk by picking up new altcoins
Like you said the percentage of successful projects is rare when it comes to new projects, currently what they give as their excuses is that their Altcoins are stipulated by the price of Bitcoin, as long Bitcoin remains bear same with their Altcoins and if Bitcoin gets Bullish then they experience a pump. All are big lies and falling for that could be a big doom as the project don't even have the potential of lasting in the market, they basically know that and will create enough hype so that more investors coming in and when it's time they sell of the tokens and that becomes the end of the project and investors capitals except those who might have understood these Altcoins and must have taken their profits at the very first pump without holding for much time.