A report by CIRP from February suggested there were 66m smart speakers in homes across the United States, with Amazon's Echo claiming a 70% market share and Google 24%.
In the time since YouTube left Fire TVs, users have been able to access the site using browsers. With Chromecast support, those with the Prime Video mobile app can cast content to their TVs and watch it on a larger screen.
Google would, of course, like you to use their paid YouTube Music or YouTube Premium services which does give you full control over the entire music library.
The native YouTube app not might have been missed, but YouTube TV and YouTube Kids certainly have, so there's something to be gained by both sides. Customer reviews, 1-Click shopping, personalized recommendations, Prime, Fulfillment by Amazon, AWS, Kindle Direct Publishing, Kindle, Fire tablets, Fire TV, Amazon Echo, and Alexa are some of the products and services pioneered by Amazon.
For example, Amazon's Prime Video has always been hard to find on Android devices.