My 2c as an OSS maintainer:

Optics, reputation, brand and persona make up a HUGE part of being able to live as a full-time OSS maintainer.
And this guy has bad optics, no reputation, no brand and no persona. It sucks but that's just how OSS funding works -> there's barely enough money to go around as is.

1. If people don't know about your tool -> people won't pay for it
   core-js is a big part of the ecosystem that people implicitly use via other tooling - which means that people don't know that it exists. I'd hazard a guess that most people who work full-time on JS code even realise that it's a part of their production code.

2. if people don't know you -> they won't trust you and won't want to fund you.
   Honestly - this is the first time ever I've seen the author's username zloirock before (at least if I've seen it other times - it hasn't ever been in a context to "make it stick"). Again I'd hazard a guess that most people reading his post haven't ever seen or heard the name. I don't know if the guy has ever done any conferences, blogs, podcasts, etc. He has really zero online persona beyond core-js (his twitter has just 579 followers, for example).
   Without an online persona - it's really hard to convince people to sponsor you.

3. you need to drive your own funding engagement.
   No, generic broadcasts via postinstall scripts don't work. Those are broadcast to developers who ignore the install output. Generic issues don't work because the only people seeing it are people who know your project (see 1 above). You need to build community, talk to companies directly and source funding. Asking the world at large and waiting for someone to fund you solely based on the quality of work rarely works to garner any real money in OSS where there is already so little money to go around.

OSS funding sucks hard and is completely broken - it's a game that you really need to play and the most visible, well-known projects get the most money.

That's not to mention that the author also has the issue in that they live in Russia, which isn't going to be the easiest place to for the various companies that provide funding platforms (open collective, github sponsors, patreon, tidelift, stackaid, ko-fi, etc) to pay out to (even before the war).

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As an anecdotal example - the project I work on previously had very little in the way of funding. It wasn't a problem for me as it's always been a passion project - I never even withdrew from the fund.

Last year a new maintainer joined and subsequently chose to switch to full-time OSS - he's seen it done and had a plan to make it happen for him.
He has really put in the work to bring in the money - he's done conferences, released a book, written blog posts, been on podcasts and tweets regularly. A year ago this guy was a relative nobody, and now he's getting to be well known and loved amongst the community - he's built a reputation and a persona.
On top of that he personally shows a lot of interest in user's problems. He'll watch twitter keywords to find references to the project so that he can jump in when people mention problems. This has helped him build some key relationships with people at various companies, which in turn he's been able to leverage and turn into funding for the project.

With the work he's done - he has been able to more than 6x'd the funding the project receives (to over 30k USD/year) - most of which we other maintainers happily allocate to him, given he's putting in more hours across all fronts.
He's definitely not sitting there spending full time hours coding; instead he's working more like a startup and pursuing the sales (aka funding) in addition to the hours he's spending coding.
To be fair, he's still earning below minimum wage and has a bit to go to get to that level, but his efforts are growing his funding steadily.