From the YouTube help page "This feature was rarely used and had problems with spam/abuse so we’re removing them to focus on other creator tools. You can still

From the YouTube help page "This feature was rarely used and had problems with spam/abuse so we’re removing them to focus on other creator tools. You can still use your own captions, automatic captions, and third-party tools and services." That seems fair enough to me. Creators can still add captions, it's just viewers that can't add them without a 3rd party service.