[0] https://archive.is/UlCpM / https://www.amazon.science/blog/alexas-head-scientist-on-con...
https://www.forbes.com/sites/qai/2022/12/06/amazon-stock-new...
Maybe the new tech worked _really well_.
Apple appears to try to make Siri an well defined interface to specific apps that offer specific services.
Looking at https://developer.apple.com/documentation/sirikit you can see specific intents and workflows that Siri can hook into. This makes it rather limited but for the things that it can do, it does. To that end, Apple isn't trying to monetize Siri - its trying to be a hands free interface to specific tasks that apps can do.
Amazon was trying to make Alexa a general tool (and they've reduced those capabilities over the years) running on AWS with additional goals of providing additional monetization routes. Things like "A book by an author you follow was released, would you like to add it to your cart?" Personally, I never found the chat more than a curiosity and even less so now that there is no knowledge engine backing the general knowledge questions.
They began as very much what you describe though, to generate pr and make their underlying ecosystems seem more attractive and advanced.