Cryptocurrency Bubble!

Allow me to be among the first to welcome you to cryptodom. This is simply how it do.
Bitcoin's community is divided, and there are far too many people who don't appear able to comprehend the workings of a PoW consensus mechanism. People are worried that there might be a chain split August first. Just because some lunatics believe that a UASF without majority miner support is possible does not make it so. Without majority miner support, a bunch of nodes will fork themselves off the network onto a chain that will probably never see a single block mined.
Ethereum is and will be under a lot of sell pressure for the forseable future - a direct result of the fact that to date the biggest use case for it appears to be ICOs, and companies that issue tokens in an ICO on Ethereum, proceed to cash out the generated Ether into fiat.
Everything else... human psychology is a driving factor. The stock market works the same way - shares of companies that have nothing to do with each other tend to rise and fall together, and if you zoom out you see that the whole market tends to behave like that. One might call it herd mentality. The only difference is crypto is more volatile.