I recommend reviewing the HN guidelines here: https://news.ycombinator.com/newsguidelines.html

Of course they won't volunteer to maintain a massive project that they depend on, when someone else is already doing the work.

But you can bet the minute core-js goes away, the community will pull together to maintain or create something new, purely out of necessity - that's the main motivator. Hopefully with a more distributed model that doesn't overload a single person.