While Bitcoin made another explosion this last weeks because of it's value more and more people searched for the opportunities to invest on the cryptocurrencies. We have seen many news like if you'd have 7$ in BTC 7 years ago now you'd be a milionaire.
Now people are aware that bitcoins value is very high and don't want to risk to invest on it because it might drop even though many do invest and believe it will only increase. Meanwhile others are investing on other cryptocurrencies that are of a lower value with the possibility of raise. Somehow etherum got on the ears of people and since it got famous and has not such a big value for the moment people are investing on it and the more they invest the more it increases (higher the demand, higher the price = pure economy law).
This is why i believe at somepoint people are going to ignore bitcoin and put their interest toward ethereum.