Because most altcoins use Bitcoin as a unit of measurement, bitcoin is the King! This time, there have been many changes to the altcoin such as: ETH, USDT, ....
Agree, bitcoin is the unit measurement of the market and whenever bitcoin drops all altcoins drops too. So this is really proof that bitcoin will always be the king.
I agree with you bitcoin is the parent or king of alt coin, so it's true that bitcoin is king