Investors won't sell too much of the coin as profits grow in bitcoin, while selling a little will still have good cash flow. This will reduce the net supply of bitcoin and increase the price. Another factor that could affect altcoins during the bitcoin halving is the overall sentiment of the entire cryptocurrency market. Because if the price of bitcoin crushes, investors will turn to altcoins. If there is a bullish trend on the horizon then a could perform well, considering that cryptocurrencies are usually matched with bitcoin. On the other hand, the altcoins along with bitcoin can lose their value if there is negative sentiment in the market.