While the value of one Dollar isn't changing much (very slowly compared to crypto) the value of one Bitcoin went up very hard (~ 700% this year). For example: If "Coin X" had a value of 10$ all the time and you put it against Bitcoin the graph would be falling. That's one reason why there is a difference between USD Target and Bitcoin. But some people want to see if there trading with altcoins brings more profit as simply buying Bitcoin and hodl ...