It would be extremely souring to me if Jekyll decided to add webpack and other javascript dependencies with a newer version. One of the things I like about Jekyll is that it's a STATIC site generator that doesn't try to do everything.
Some sites I want to be dead simple, and that's what you get with Jekyll. If I want more complexity I'd go with a more complex generator like Hugo or Gatsby.
That's my impression as well, as an outsider.
A recurring nightmare of mine as a maintainer is that I'll wake up one day and read someone's blog proclaiming the death of one of my projects, when all I've done is stopped adding new features to it. Especially so when it's someone who's made a living for themselves as a downstream user.
And I'm in the same boat as you: I've had a Jekyll-based blog, without incident, for a little bit under a decade now. It's only gotten faster and easier to use over time, which is more than I even asked for.
Changes are very rare other than occasional bug fixes or breaking ecosystem changes, but that doesn't mean the code is bad.
The code is a hammer, you don't need the newest shiniest hammer. You just need the hammer that hits nails.
If I want an SSG, I want an engine that takes a relatively simplistic text markup format, like Markdown or Org, and create a series of HTML documents from it. Why would the technology that does the gruntwork matter to me as an user?
Also, with Jekyll's plugin structure, what is an example of a functionality that cannot be achieved in Jekyll, but can in another non-Ruby SSG?