Bitcoin is king because :
1) It was the first crypto coin. People associate crypto with Bitcoin.
Bitcoin was not the first crypto coin to appear, but Bitcoin was the first crypto coin that succeeded in capturing a lot of public attention so many people thought Bitcoin was the first. The first cryptocoin was eCash which was developed by the DigiCash company in 1990
https://www.investopedia.com/tech/were-there-cryptocurrencies-bitcoin/Thanks for sharing the information. Before now, I never knew that there were cryptocurrency before the creation of Bitcoin. Now I know better and one thing that stood out is that fact that Bitcoin is the oldest surviving cryptocurrency as the others died according to the source you gage.
While not the first cryptocurrency, Bitcoin is the oldest surviving one as it was released via a whitepaper in 2008.
Base on the above, the caption is not out place, Bitcoin still remain the king. It drives the entire market and also have wider acceptance which is still increasing everyday as seen from the Bitcoin dominance that is above 50% as of today.