YouTube is pulling support for Amazon’s Echo Show and Fire TV due to a lack of reciprocity.

However, Amazon also added a redirect to the YouTube open web presence to Echo and FireTV. It is this access that Google is cutting off.
“We’ve been trying to reach agreement with Amazon to give consumers access to each other's products and services,” a spokesperson told the Verge. “But Amazon doesn't carry Google products like Chromecast and Google Home, doesn't make Prime Video available for Google Cast users, and last month stopped selling some of Nest's latest products. Given this lack of reciprocity, we are no longer supporting YouTube on Echo Show and FireTV. We hope we can reach an agreement to resolve these issues soon.”