Pure speculation
I've been invested in and watching ETH since around of February-ish. It's market cap was still under $2 billion and it was just about to take off. And then it did.
Since then it has become pretty clear its market cap will soon overtake BTC's. As of this writing BTC stands at $43,740,815,196 and ETH is at $34,719,350,062. ETH's growth continues to outpace that of BTC.
When ETH market cap surpasses that of BTC I suspect there will be a lot of mainstream media coverage (heck, ETH has already had a fair amount of coverage), and even more interest in it. I'm guessing there will be a nice short-term bump in ETH.
I'm invested in ETH for the long term. I truly believe in what they're doing. But happy to see any short-term bumps too. :-)
(Note: I'm excited about all crypto, please don't take this as a ETH over BTC post. It's not. It's just an observation and a thought I've been having about market caps.)