This is why all Alts follow BTCs movements.

It is pretty clear that alts reliably follow BTC's macro price movements. Lots of people still ask why this is and they end up being told variations of "Because BTC is the leader" or "Because BTC is the main currency they all trade against" or other non-answers like that.

Here is why alts follow BTCs price movements:

1. Imagine Eth is worth $700 USD and 0.08 BTC
2. BTC starts losing value.
3. As soon as it starts losing value, that 0.08 BTC valuation of ETH is worth less than $700 USD valuation. ETH's BTC valuation either needs to go up (0.081 BTC etc), or the $700 valuation needs to go down ($699 etc). Either movement is fine, and if the market was confident that ETH was worth $700, then the BTC value should move up. But the market really has no basis for confidence in any crypto prices so it is free to move either, or both. So it typically does...
4. Before anyone thinks about this let alone has time to react, arbitrage bots sell the ETH for USD and buy ETH from BTC and lock in the value difference between the two prices, pushing the USD value down, and the BTC value up.
5. Real people (and other algorithms) see ETH price suddenly drop for no apparent reason (they may see BTC doing the same, which would only reinforce their fear because they know it "leads" alts), they fear the worst, and panic sell to avoid further losses causing the market amplifies the initial signal, feedback ensues, and you get larger movements in the alts than you get in BTC.

So, from an initially weaker arbitrage forced movement based on the difference of BTC/USD valuation, the market over-reacts in an attempt to beat the rest of the market to the sell off/buying of the alt coin which they know is coming because BTC is already doing it.