They're not worried about competition in the video captioning market because they're not a video captioning company. They're probably losing money on the feature and are happy to offload the work to someone else.
I mean, Google kind of are a video captioning company. Google Video was created with the goal of letting you search videos by indexing the automatic textual transcriptions of their audio content. YouTube still performs that role for Google Search; that's why Google's automatic transcription is as good as it is already.
