Es porque tienes que monetizar el canal.
Buscando con mis colegas de curro hemos encontrado esto:
Marissa - Community Manager said:
Hi all,
I wanted to provide an update on this thread regarding the inability to link your associated website. Following a recent change, your channel needs to be enabled for monetization to link to your associated websitefrom cards and end screens. This new requirement gives us additional information to determine the validity of a channel and it allows us to confirm if a channel is following our community guidelines and advertiser policies. If you’d like to link to your associated website from your videos, please follow these steps to enable your channel for monetization.
If you’ve already set up cards and end screens that link to your associated website, these will continue to show. However, you don’t have the option to edit them any more, only to delete them.
We know this is frustrating for some but external linking is a powerful tool that provides relevant information to viewers, and therefore, we want to ensure that the creators showing these links are playing by the rules. Requiring monetization gives us additional information to determine the validity of a channel and its compliance with our policies.
Thanks,
Marissa