I think of bitcoin as dollar currency while altcoin as currency of other country. Currency movements of other countries refer to or pegged to the movement of the dollar, if the dollar rises then the euro, yen, won, etc. will also rise. Bitcoin as the first coin has the highest position in the cryptocurrency hierarchy, if there are external factors such as the rise of some countries prohibit bitcoin, then investors will be busy pulling the money in bitcoin, if the amount of bitcoin volume drops then the price will also decrease, straight with altcoin