The petition expresses support for the National Popular Vote Compact, an interstate agreement. Once enough states sign on to that agreement, they will pledge to award all of their electoral votes to the winner of the nationwide popular vote.
Coalitions change, and it’s possible that effectively abolishing the Electoral College will not always help Democrats. In the short run, however, it certainly would.
Further confirmation — if you needed further confirmation — that “building the political power of young people” is Rock the Vote’s way of saying “help Democrats.”