Custom assertions use primitive comparison, not assertions

https://assertj.github.io/doc/#assertj-core-custom-assertions-creation shows how to create custom assertion classes. One part that I find very confusing is this piece of code in the custom `hasName` assertion implementation:
```java
// check assertion logic
if (!Objects.equals(actual.getName(), name)) {
failWithMessage("Expected character's name to be <%s> but was <%s>", name, actual.getName());
}
```
I would expect to reuse existing String assertions there, e.g. to write this instead:
```java
// check assertion logic
Assertions.assertThat(actual.getName)
.withFailMessage(() -> "Expected character's name to be <%s> but was <%s>", name, actual.getName())
.isEqualTo(name);
```
Is there a good reason to not use other existing assertions there (like confusing the logic to shorten stack traces or similar internal things)? If yes, can we please document it? Otherwise, shouldn't we change the example code?

I typically _do_ use existing assertions in my own assertions, and I have this nagging feeling of doing something wrong without knowing what exactly. :)