This is tough because the developer is clearly very passionate about his work. As someone who works in the industry, and having used core-js myself, I certainly have an appreciation for all of his work and effort. Unfortunately, he wasn't able to secure proper sponsorship and funding to keep doing the kind of work he wants to do. Open source projects die all the time, it's not a sustainable pattern of operation without proper sponsorship. I think he feels a sense of responsibility to keep the library up to date, given how instrumental it is to the industry (which I can attest to), but it can only take such a toll on him before he lets it go. He should not feel like he let anyone down if he lets the project die. The industry leeched from his efforts long enough. Someone will fill core-js's place eventually, once the need is strong enough. ¯\_(ツ)_/¯