Siri Search is already a thing - the equivalent of "Spotlight" in macOS is branded Siri Search for iOS. From Apple's perspective, Search should be an integrated part of the user experience - if the task requires search, then search occurs. No "going to Google" (or Bing, Duck Duck Go, etc.) as a separate act or destination. It's not just a matter of searching the web, but searching all your data, contacts, email, text messages, media, apps, etc. for what you desire.
Google's model is built on offering a useful, free service to draw traffic that can reach users of any platform. There's nothing intrinsically wrong or "commercial" about search. Web search has simply become commercialized. However, Google search is, by its nature, an external search. Would you grant Google the right to crawl the contents of your hard drives and iPhones?
Apple's model is product-as-service. By making their devices incredibly useful, they keep selling more products and encourage repeat business. In an environment where search becomes nearly invisible and ubiquitous, there's no need to "search" as a separate task/function. Whether given as a spoken command or a typed text string, search is simply delivered when needed.
Privacy is key, of course. Google's business model nearly demands that all search processing occur server-side. There are certainly benefits for the end-user in terms of search quality - the better Google understands your needs, the better the results. However, we know Google also uses that knowledge against us by selling the fruits of that knowledge to others. Apple, on the other hand, is doing far more of its work on the local device. They're selling us the processing power and reducing their need for server-side investment. The better my iPhone and Mac "understand" my needs, the better they can serve me.
It's not a surprise that Apple would want to improve the quality of its "external" (web) search. Apple is already in full control of internal search. If they don't have to defer to a third-party for external search, so much the better. If my Apple devices delivered a useful, truly non-commercial web search result (no ads at the top of the list, no sites buying their way into a better position, etc.)... count me in!