However, I guess what made it appealing initially, was that it uses a syntax known to a lot of web developers. The callback pattern helped.
Although these days, we have been moving away to generators or async-await.
This is the key. And it reflects poorly on them for that. Syntax is the easiest part of a language to learn. The nuances of behavior is the hard part - and those nuances change as you move from the browser to the server; what makes good browser code will not make good server code.
In reality they shunned a ton of knowledge and community support to keep a particular (and particularly mediocre) syntax. Even today, years after Node has reached popularity and many lessons have been learned, developers with no experience outside the browser think they can write perfectly good server code, simply because they know the syntax. Never mind that all of the design patterns change. Never mind that the core libraries they use change. Never mind that they suddenly have to be cognizant of how much CPU time their code takes.
This is really true and it's sad, because it leads to more security problems on everyday software.