Man, even btc worth 0. What it should be used for ?
You can see that bitcoin is kind of worthless in all the advertisement of the coins (fast transaction, secure/anonymous payment, border less payment...). All of those thing, you can find a simple coin that do much better than bitcoin.

But why bitcoin is still expensive ? why it is still king of the cryptos ?

I guess the value of the coin is something that people accept that it will be.