This has been a bit different this time. Usually when BTC goes up, it drags the other coins along with it. Not so this time- the interest seems centered on BTC. Some of it I suspect is people "buying the rumor" of the ETF. Also there's been interest from institutional investors- I read that Coinbase is setting up a seperate platform for the big money guys which will be attractive to Wall St. as it provides some sort of safety net.
Mostly, however, I think it is because of me! I got tired of watching BTC fluctuate between $6100 and $6600 so I dumped my BTC and bought altcoins, so naturally BTC decided to rally. At least I got to dump most of my alts and get back in at around $7300 after doing pretty good with them.
Haha that is how it seems to work for me as well.
In all seriousness though, this same pattern happened two times in 2017, where Bitcoin sucked all the value from altcoins and went up while they crashed.
However, in both cases, alts eventually went up as bitcoin increases slowed.
I call it my Kiss of Death. Every time I bought a coin it immediately went down... I found one that was $0.01 so I figured it can only go up. It didn't- it tanked completely!