Trait with blank constraint on lifetime

Question

This code (derived from a more complex example) compiles [playground]:

fn func1<'a>(s: &'a str) where 'static: 'a { println!("{s}"); }

fn func2<'a>(s: &'a str) { func1(s) }

trait MyTrait {
    fn func<'a>(s: &'a str) where 'static: 'a;
}

impl MyTrait for () {
    fn func<'a>(s: &'a str) where 'static: 'a { println!("{s}"); }
    
}

fn main() {
    func2("hello");
    <()>::func("world");
}

but this one does not [playground]:

fn func1<'a>(s: &'a str) where 'static: 'a { println!("{s}"); }

fn func2<'a>(s: &'a str) { func1(s) }

trait MyTrait {
    fn func<'a>(s: &'a str) where 'static: 'a;
}

impl MyTrait for () {
    fn func<'a>(s: &'a str) { println!("{s}"); }
    
}

fn main() {
    func2("hello");
    <()>::func("world");
}

As func1 and func2 show, constraint 'static: 'a appears to be a blank constraint. So why is it necessary when implementing the trait?

---

Further comment on the question: if this is a simple signature problem relating to where clauses, why does this example compile? [playground]

use std::fmt::Debug;
trait MyTrait<T> {
    fn func<'a>(s: &'a str) where T: 'a + Debug;
}

impl MyTrait<f64> for () {
    fn func<'a>(s: &'a str) where 'static: 'a { println!("{s}"); }
    
}

trait MyTrait2<T> {
    fn func2(s: &str) where T: Debug;
}

impl MyTrait2<f64> for () {
    fn func2(s: &str) { println!("{s}"); }
    
}

fn main() {
    <()>::func("hello");
    <()>::func2("world");
}

and not this one: [playground]

use std::fmt::Debug;
trait MyTrait<T> {
    fn func<'a>(s: &'a str) where T: 'a + Debug;
}

impl MyTrait<f64> for () {
    fn func<'a>(s: &'a str) where f64: Debug { println!("{s}"); }
    
}

fn main() {
    <()>::func("hello world");
}