I can understand the choice as an example for @Stable: it highlights that this addition even comes with "free" upgrades for (some) existing code out there, and it immediately shows a concrete use case. But yes, they could have gone further into generalizing from there.

If you mean the headline, Strings are a universal data type across programming, so claims of improving their performance gets more clicks than "this annotation that you have never heard about before makes some specific code faster", especially when it comes to getting the attention of non-Java programmers.