Well, I write Java and C++ for a living. Maybe that's the same as COBOL if you're a front-end JavaScript developer? What, exactly is there for me to "stay up to date" on?

I'm not saying that you should never learn anything new. For example, I really hope that I have a chance to ditch C++ and Java both for Rust one day, but I can't just go and do it today and that's fine. Change does not need to happen at the pace that some people seems to think it does.

I cannot provide any examples for your languages of choice but mine (CL) is older and I do check out new libraries.

And yes, I would be pretty irritated to find anyone in my team who thinks there is nothing else for him/her to learn, even in their field of expertise.

Who said anything about "nothing else to learn". There's always lots to learn, or I wouldn't have a job anymore. That doesn't mean I spend any real time reading or using other peoples code. Most of the actually interesting work I do involves things for which there are no libraries. The less interesting thing (e.g. a REST service using Spring) do their job just fine and are so utterly boring I can't imagine why anyone would care enough to rewrite the whole service in some other framework.

I do go looking for libraries when I have a need for some functionality, but I don't seek out new libraries to replace other libraries or my own code when the existing solution works. It's the frequent rewriting of working code to use some new tool/framework/library just because it's new and sexy that I find problematic.