Bitcoin made big gains in the beginning because of its structure and concept. After a skyrocketing price was obtained, I believe that the "powers that be" or those that print, mostly digitally create the world reserve currency, decided that they could purchase large amounts of Bitcoin. Therefore drive the price even higher and begin to gain some control in a system that they have no control over.

See when crypto currencies finally put themselves in a position where the public took notice, they also had to make a move that enabled them to retain the freedom of markets they were designed to do in the first place. This is about the time period when Bitcoin split and created Bitcoin Cash, like all good strategies, the split was said to increase the size of the block, and therefore make transaction times faster, which it did. But it also created an alternative angle for the people that were there in the beginning, that truly built the structure. They all received Bitcoin Cash based on the amount of Bitcoin they held, but only when the split took place. Everyone spending huge amounts of currency to get in afterwords were out of that loop, and therefore had to purchase Bitcoin Cash separately. Most other Altcoins really started springing up at this same time period, and could very well be following the same strategy. MOST, not all, obviously coins like Ripple appear to have a counter intuitive agenda.

Part of the idea behind Crypto currencies was to eliminate the banking system as we know it. Until that system is taken down, the bankers will always create there power out of thin air and manipulate any and every system that remotely stands in there way. As long as they can purchase in U.S. Dollars, Japanese Yen, or any other currency they can create for nothing, we'll have a constant cat and mouse game taking place. Take a look at this link from the Dodgecoin builder..
https://motherboard.vice.com/en_us/article/9kng57/dogecoin-my-joke-cryptocurrency-hit-2-billion-jackson-palmer-opinion