Earlier quoted context omitted.
>> even though the thing they are using is still well maintained. I think you mean "even IF the thing is still maintained". This is a big IF. Something as ubiquitous as a React app may still work fine after a few years, but try updating or fixing something and you're in for a world of hurt.
In my experience dealing with the tooling is fine for ongoing projects by just checking for updates every week. But it is very stressful to update from Webpack 2 to 5 for example. So taking an old project from a couple of years ago and updating the dependencies is not that easy, especially if you were using a lot of the build tools features.
Upgrading dependencies can be a trap. Like, in the past, I've delegated a bugfix that shouldn't take more then an hour or two to a co-worker, only to see them waste an entire day in dependency / NPM hell.
To my mind, there needs to be a compelling case or argument that justifies sinking time in an upgrading exercise.