I also notice the shift you are mentioning.
But I'm still a bit hesitant about its causes. Wether degraded search is an intentional feature or not, I think there is another and simpler explanation to consider when we discuss this topic: cost and skill.
Google seems to be an exception in that field as it has, in my opinion, clearly demonstrated an ability to implement a functioning search. Consequently, our only option as users is to assume that a dysfunction in a Google product's search function can only be intentional and triggered by hidden motives (e.g., restricting users liberty to decide what should never or absolutely be in the results).
A second factor I like to take into consideration is the iPhone user effect, or what I like to call the "iTard effect". The itard effect is the tendency by tech companies to design and aim their user interfaces specifically to satisfy their least tech savvy users while alienating its more technical customers in the process. A good example of these are search engines that automatically canonicalize what you type and either won't allow you to run a search exactly as you specify it but will keep altering your query terms because "you probably needed help writing this query".
There is also a third option, that affects both larger tech tycoons and other companies: they cannot search their content accurately.
This could be caused by poor architecture decisions (I think we are still years ahead from assessing the real damage caused by over-containerization/micro-architecturization across the world) but also by costs: the more you delegate your IT operations to third parties (e.g., cloud, pass, saas, etc.) the more you become vulnerable to abusive costs of search.
I totally agree with you, search simply doesn't work in most of the websites I regularly visit (even search engines). But I think there are only less than
a dozen companies that would intentionally and effectively alter search results to impose their own agenda onto the user. Unfortunately, these companies are precisely the ones that interact with the vast majority of human beings on the globe on a daily basis :)