Fundamentally, the growth in the cost of bitcoin is not supported by anything. Its price is the result of speculation. He took a leading position, because he first entered the market. But the main task of the crypto currency as a payment instrument is to ensure fast and safe circulation of funds, and not to increase the rate at all. Bitcoin in this sense no longer meets the requirements for the largest crypto currency in terms of capitalization. It is rather a bubble, manipulation, speculative tool.
Actually if you look at the data you come to a different conclusion, bitcoin is used more than any other coin in e-commerce, despite the fact that there are newer coins around, easier to use blockchain interfaces (wallets) and faster transactions. Dash is a good example. However transactions are a fraction of bitcoin in e-commerce. The big questions is, why?