Alts had their day during the Altcoin season throughout February and March, now those alt gains are being rotated back into BTC.
This was the standard cycle during the last bullrun, which makes me think that the market cycle has changed (see my post on that subject : https://steemit.com/introduceyourself/@onefreemanwins/introduceyourself-who-i-am-and-why-i-think-it-is-likely-that-the-bear-market-has-ended)
Please note that the 6.100$ BTC price was on Bitfinex only and due to the Tether scare premium.
The price on other exchanges is closer to 5.700, so we have not cleared the significant resistances on the way to 6.100 yet.
One could argue that alot of this pump is people buying up BTC with their Tether on Bitfinex and withdrawing them due to the current uncertainty on that exchange.
My guess is that the major alts will have their day again, the art is in picking up on the change of season early on.