> search advertising of any kind requires a search engine with sufficient scale to make advertising an efficient proposition for businesses.
So does creating OSs. Let me make a similar statement on OSs: "selling OS of any kind requires certain scale with sufficient number of apps, for manufacturers to bundle your OS and app developers need the scale of OS to make it worthwhile for them to create apps".
Remember Windows Phone Catch 22. They created an OS which was reviewed well, seemed like a fresh take on UIs. But apps didn't come or came late, often buggy and not fixed in time. In the end it was never able to compete on apps.
> Specialized search engines require significant investment, including the cost of populating and indexing relevant data, distribution, developing and maintaining a search algorithm, and attracting users.
Didn't Siri and Alexa do exactly this to entrench their position in market. In fact voice search engines(assistants) often come as non changeable defaults.
In case of Siri it comes by default on more than a billion Apple devices.
The only way we exclude these from our discussion is if we go by a very narrow definition of search, these are here to stay and will possibly dominate search behaviour.