Your Java example hits too close to home. I know Java pretty well, and despite several good interviews, I got rejected because I didn't know Spring. One company even told me to learn Spring, build an independent project on it, and come back to interview. They followed up with me for 3 months after that till I told them not to anymore. At that time I was proficient in Java, Angular, Typescript, C# & Jython.

Ironically - I got hired into a product company which mostly works on their own internal java frameworks and didn't have a spring requirement. I figured I'll have to give time to learning Spring on the side since most Java jobs require it, but my first project here was on Spring Boot/Hibernate/Angular because of a client requirement, and I was put on it purely because of my Angular knowledge.

I'd understand if a company required complicated stuff done in Spring/Hibernate, but most organizations use of Spring Boot is limited to building rest APIs, for which no previous knowledge is necessary. I haven't yet run into an issue I couldn't solve by less than an hour of googling despite having no experience in it beforehand - even making interceptors and adding Spring Security.

Because of its simplicity I do wonder if I've barely touched the edge of it, and the usual usecase is much more complicated than this, but I'm planning on learning spring on Udemy anyway, so I guess I'll find out.