Yes this exists, but again introduces a new thing into PHP, rather than using an existing thing. Instead of using existing function syntax and leaving away the name, now one has 2 more things: The "fn" (why can this not be "function" which already exists?) and in combination with "=>". So it is similar to "function ... use ..." which also has the need to introduce a new thing, the "use", instead of simply capturing its environment.

The point is, that the designers of PHP decide again and again to add another wart, rather than designing the language in an extensible way. Here a little extra, there a little extra, here a new keyword, there a new thingy. Compare that with other languages. Even JavaScript has managed to have simply the same syntax for functions and anonymous functions. Although it did also introduce an arrow syntax. However it's arrow syntax is not really needed, even though shorter, in contrast to PHP, where you need it, unless you want to list all the parts of the environment you need in the anonymous function. At least in JS they didn't introduce a new extra thing like "fn".

I don't think the design of PHP is done with good oversight. It is done with the approach of tacking things onto what exists, in the easiest way they are able to do, without any goal of keeping the language concepts and keywords minimal. Designing something like "fn" or "use" is a hack to make implementation easier, because they are previously unused keywords, that will then make it easier to adapt the parser for the language, but these decisions are offloading mental load to the user, which ultimately is a bad design.