It sounds to me like you would like a "batteries included" version of Perl 6. (include JSON/YAML in the runtime)
No. We only include things as part of the language where the design of it is immediately obvious, and is useful for many applications. It also helps if it has been proven in other languages. So Promises(Futures) are in there, but many other things are not. You can do anything in a module, so write an external module for it instead.
Otherwise we would have the problems where the best module for the job is not in the runtime, but everyone uses the one that is in the runtime.
I have heard that Python has this problem with HTTP. Think of it like this, a module for doing X is included with the first version of a language. That means it is a module that was not written by an expert, because at that point in time there was no expert in the language. Everyone uses it though; as you don't have to install it, because it is already there.
We don't have an official module manager, because we want all of them to be equally as official as every other one. It is a good thing too; as most people in the know use zef currently, rather than panda. If we had one that was official, it would have been panda.
That's also why there is not, nor will ever be an official implementation. Any implementation that passes the test suite is just as official as every other one. (although there is only one currently)
Basically you are asking for things to be included, that are specifically not included for very good reasons. The way that this is dealt with is by using the idea of distributions like "Rakudo Star" for Perl 6, or "Strawberry Perl" for Perl 5 on windows. That is an implementation of Perl 6 along with a set of useful modules.