I don't agree that programming expertise is fragile. There is a kernel of knowledge that transcends language and syntax, and that is by far the bigger part of "programming knowledge", much more important than knowing specific syntax and how to use certain tools. For more, see [1].
This doesn't mean you aren't correct. People may still be reacting negatively to change, because it does require work to learn new libraries, frameworks and languages. But that is not the same as saying that programming expertise is fragile.
I'm going to have to disagree with you, especially in relation to large frameworks.
I spend a lot of time working with medium to large ruby on rails applications. I know them very well and I am pretty good at doing things quickly and correctly. If I have to work on a php, python, or javascript project, it takes me one or two orders of magnitude longer to get things done than it would in a rails application.
The ability to start working with a new language after reading a blog is useful but it doesn't mean you'll be effective and useful in that language in a week.
A person with the ability to program, probably will have that raw ability in various languages. There is a knowledge core that is very transferable. An experienced programmer can come up to speed very quickly as concepts get mapped into things they already know. A polyglot will have been through this several times, and won't be afraid of the process.
But there is a great deal of knowledge that we use every day that is environment dependent. A programmer with 20 years of experience in various languages will not be noticeably better by day 5 in a new language than someone who has been programming for 2 months only, but in that language. A simple change can leave a programmer feeling incompetent.
Programmers who respond to this badly are not going to handle such transitions well. Furthermore if they get stuck in defensive behavior, then the initial discomfort will turn into permanent failure.
This doesn't mean you aren't correct. People may still be reacting negatively to change, because it does require work to learn new libraries, frameworks and languages. But that is not the same as saying that programming expertise is fragile.
[1]. "Programmer Knowledge" http://henrikwarne.com/2014/12/15/programmer-knowledge/