I never worked on TilEm proper
For the past 9 years and a half, or so, I've been the official maintainer of the libti* family created by Romain Liévin 20 years ago, and Benjamin Moody, the main author of TilEm, has effectively acted as co-maintainer of libti* for most of my time as the official maintainer.
In some cases, such as small entities, or small IT departments in larger entities, sysadmins do indeed make it possible for the whole company to run.
I guess I got into part-time, sometimes near-full-time sysadmin work, without receiving training, for a variety of reasons:
* working as one of the few full-time software developers / computer engineers in a computer-oriented, but small, entity. We used a set of computers, which needed to be installed and administered;
* working on a R&D project in a large IT company - again, we had a growing set of computers, in a peculiar environment, and I want to try and make a good job, and I like learning;
* being pulled out of said R&D project because, you know, money restrictions, and becoming an available
resource on the local workforce, right when a pure sysadmin project for a customer started and they were looking for people. No money to spend on training, even though neither of the two of us non-sysadmins mastered any of the technologies involved in that project. We had never
used most of them in the first place, and we were tasked to make a streamlined environment for near-automatically installing from scratch (down to fully automated, non-networked OS / hypervisor installs on bare metal) and performing the initial configuration of a set of computers and VMs. Nothing in that process can rely on Internet access, because that proves not to be always available in practice when the install + initial configuration procedure is set to be performed. Unsurprisingly, we learnt a lot
You're right, most people learn best, with the highest motivation and ability to remember, when they're studying on their own, or they have to solve a work problem. What one learns on their own, during their free time, can clearly make a difference when trying to get an internship, or a first / the first few jobs - it did for me.