Broadly I think people tend to under-estimate how many browser bugs and quirks jQuery normalises/works around; and anecdotally their assumptions about which browsers is usually wrong too (dropping the older IEs in v2 did not lead to the massive size reduction people expected).
Plus when you really get into it, ES6 replacements have their own quirks, eg. I was tripped up by the way the queryselector methods handled queries that returned zero results. jQuery just smoothed that kind of stuff over.
With all the focus on virtual DOM frameworks, it's not entirely surprising that no strong successor to jQuery has appeared... but I think there is space for an ES6 helper library that normalises things similar to the way jQuery does. That could be jQuery itself but with a year to go before we're likely to see jQuery 4, it may have simply moved too slowly.