Crypto has its cycle which traders follow, Its not always crypto follows Bitcoin movement because sometimes altcoins move into opposite direction. Altcoins price most often Bitcoin is because other traders that late on riding in Bitcoin gains usually look for other invesment which is altcoins to start or ride the wave that Bitcoin start. The exchange has a trading bot too which reacts on Bitcoin sudden price movement which gives an profit for stabilizing all the crypto price in proportion with Bitcoin gains.