I wonder how much of it is low-level experienced developers only ever using C fail to see that C is not the universally best tool (or, 'if all you have is a hammer, everything looks like a nail' question).
I'd say that's it. From my own experience with software developers, convincing some of them to learn something new is practically impossible.
If the person in question has a true passion for the craft, you can regardless of the age/seniority of the developer (at least in my experience). In fact, learning something like a new programing language is a big undertaking and if your work doesn't offer incentives/rewards the will has to come from the person him/herself and so that's why the passion bit I mentioned above.
In my experience I also notice that more senior/older devs are more reluctant to learn new things, but I am unsure if that's due having their passion destroyed by many years of bullshit companies politics, pointless meetings/trainings, and adherence to the latest flavor of agile development every quarter or simply an age thing (I'm not there yet and so I can't tell first hand).
Suck here is more of an emotional thing. They can output high quality code fairly quickly. The issue is not knowing all of the quirks of the language and all development being slower and more difficult.
Dropping down to simpler tasks while learning the language is a huge ego blow.
It was a good argument literally a couple years ago less a few weeks before the chatgpt first release. Nowadays it's basically a moot point.