It does not make any sense ...
the coins are doubled and 300-600$ is added to the value
does not make sense imo
I really don't think that it doesn't make sense.
When this happens it just means that bitcoin is going up even more than it should be. If you think about it, when bitcoin is stable but BCH goes up, in theory bitcoin is actually going up as well.
But this correlation between BCH and BTC price isn't going to last forever. Even though it's an airdrop there is only going to be a certain amount of time when the two currencies have an inverse relationship. BCH is already recognized as an altcoin more than it is a fork of bitcoin. In the future, BCH is going to be something similar to clams, another coin issued by blockchain snapshot.