Metadata in angular

I'm trying to wrap my head around Decorators & Metadata in Typescript and thought angular would be a good project to look for some kind of best practise.

In the old versions (e.g. 2.1) they are using DecoratorFactories and inside they apply metadta over the reflect-metadata API proposal( http://ift.tt/2AERHRU)

In the new versions they started implementing their own system for the decorators(http://ift.tt/2yuQY49) and just appended the data to the constructor where it is easy accessible. Like:

@SomeDecorator(someDataObject)
class SomeClass { ..... }

console.log(SomeClass['__annotations__'])
console.log(SomeClass['__paramaters__'])
console.log(SomeClass['__prop__metadata__'])

Someone has any idea why they are doing this? Advantages? Disadvantages?