Bitcoin is the original currency. Like gold it will always be a back up when the rest struggle. So it makes perfect sense that when the alts are going down then people will move their money to the more stable and valued bitcoin.
In the long term I see it acting like a reserve to hold the value of the market as people will have most of their money in the more useful and purposeful alts like steem and ripple. It will always be there holding up the market but more as a stop gap than a functional entity.