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/2) It has a solid foundation. Developers made this coin with long term vision.
It is true that Bitcoin has a strong foundation and that is in its solid community which continues to develop this coin well so that many things arise to bring down this coin to no avail because the market still makes it the main choice in the market, so far it is true that Bitcoin is the king of dozens of existing coins.
3) It is a good option for current investors alao because it proved its worth in last 13 years.
Other coins that appear are only developed for the purpose of enriching their developers, that's why you will see how many trash coins appear and when they first appear they are always said to have potential but the passage of time proves that they are really trash coins. Bitcoin has been around for a long time and those who believe in its future development will get the opportunity to make good profits from investing.