It is a general convention that in order to see the price surge, the total net inflow have to increase. Suppose there are 20 million Bitcoin and total market cap is 40 million, then each BTC would be priced at 2$. In the same way, if the total market cap is 20 Billion, then each bitcoin would be priced at 1000$. So, the more the market cap for a particular coin, the higher its price would go and henceforth, every time we see a rise in price, the total market cap also increases simultaneously.