The answer is easy, the only thing is that altcoins have a lower price than Bitcoin,
yes you can say 90% of altcoins have a low ROI, so to invest safely, of course, altcoins are the second choice after bitcoin,
some even make it the first choice, just like me who choose altcoins to be the first choice of investment.
altcoins might have lower price though it usually have higher ROI than bitcoin honestly.
so saying it has lower ROI is wrong, after all you would rarely see bitcoin multiplying its current value to hundred folds but altcoins could just do that.