Well first of all if you notice the swings of the alts are coming a few days after, wait for bitcoin to go up, and then sell your bitcoin to buy alts, then wait for them to go up and bitcoin to go down and do vice versa. I mean if you see a clear pattern. :)

Yet I don't just think it has to do with the fact that coins cannot always be traded without having to go through bitcoin. I mean the current valuation of bitcoin if I would sell STEEM wouldn't affect the price that much. I buy bitcoin for lets say $8000 and sell it one second later to transfer to euro's.

I think it has more to do with the fact that most people believe in bitcoin as a thermometer for all the cryptos. Therefore if it does bad, all cryptos must do bad, which is why we are seeing these fluctuations.