The fact this doesn't happen very often is a significant failure of the tech industry.
It's happens considerably more than you could imagine, but most of these businesses don't market the way Twilio does. Many create niche tools you're probably just not running across (Palisades Monte Carlo Simulation for Excel, Minitab stats workbench, the legion of paid Magento/WordPress/Platform X companion tools).
Not unlike how a vast majority of professional programmers don't work for FAANG, but we pretty much only hear about FAANG.
Replacing customers with people emotionally engaged to support you is an exploitative process, involving the takeover of people's mindshare, in a way that can be compared to indoctrination.
People rationalizing the means of this indoctrination is deeply disturbing.
What I am talking about is the rationalization of making "fans", increasing engagement and the promotion of "whale" systems. Those lead to the problem I discussed.
At the end of the day, you need to get by. If you want to live off the things you love you will most likely have to adapt to your audience and do sales like everyone else. Might not be an idealist's dream, but it's how humans work. Doing digital stuff doesn't make fans or customers change how they value things. Besides, giving away almost anything for free upfront raises the bar for people to pay anything at all. It's how we work.
But me now is like "why the hell would I give that kind of money to some rando on the internet that stream games?". My patreon career is limited at giving a podcast creator $10/month and that was hard to justify for myself.
Still, he didn't give all his 1k to the same artist. Mainly because most artist launch at most 1 new album per year?
You can sell software development services, and your fan may be a graphic designer who uses you every time to build out the back-end for the beautiful designs they make. You do a good job, you're their go-to person, they are your "fan".
The article mentions professional training and education, which makes sense.
I can also see certain people spending that kind of money on physical goods (mechanical keyboards, audiophile equipment, one-of-a-kind art pieces) but $1k of revenue from physical goods is very different from $1k of income.
Other than that, the only things I can think of would be direct access to a celebrity or some form of conspicuous consumption. ("That game you play all day? I personally cover 40% of its operating costs.")
I don't see how the average webcomic artist or food blogger can achieve anything like what is described here.