Altcoins follow bitcoin most likely because of  Bitcoin is the king of crypto world. Bitcoin is the oldest Cryptocurrancy currency, and it is also the most successful currency with the highest potential and value, in addition, the Bitcoin market is the largest among the Cryptocurrancy market. So it is only natural that Altcoin follows Bitcoin and is influenced by the market and its price. All cryptocurrancy now move up and down at the same time. Just as prices are controlled by one group.