@mandrasch I've been in a Job working with Spring Boot for a couple of years. It's a framework and that takes time to learn especially when it comes to practical scenarios.
Overall to me it's more a question about the Java / Kotlin specifics. Security for example looks like Symfony. Java and PHP 8 look more and more alike, but still: you need to know the ecosystem and Java's ecosystem is huge!
In my experience Spring/Boot projects tend to overuse Microservices more than PHP based projects do.