I will answer according to my present understanding... maybe some veterans can chime in on this one. The bitcoin is the strongest and the leader among cryptocurrencies. It is very strong against the dolar as you know. And it's value against the dollar has a huge effect on the rest of the top 20 crypto currency's. Steem is just one of the top 20 crypto currency's. The steem/USD is very dependent on the BTC/USD.
Hope that helps... resteem this and let's see if some big boys can come and help answer this :)
Thank you @yoda1917 for helping to put me in the picture. As such, based on your reply, it seems that there is more of a Bitcoin influence but not absolutely so..
I did resteem to all 78 followers and I trust that somebody will resteem it themselves also - this concerns us all - even non-investors such as myself*. ^_^
(* Although I have been mulling over the possibility of powering up my account in what little way that I can - STEEM all the way!)