That doesn't make sense. Why would someone who knows how to find a different search engine, change the setting be part of the group of people who are new or otherwise clueless?
I have to assume you're not trolling, and really can't conceive of an entire large category of people who might, in response to a Facebook post, follow step-by-step instructions to change their default search engine without understanding the ramifications thereof, or how to change it back.
There are more people in that category than in the category of people who change their default search engine for good reason, knowing that it may deliver a less-optimal experience than Google under some circumstances.
Interacting with humans has shown me many, many examples of people who can follow steps written by a marketer to push their nonsense without any clue of how to reverse the process.
What doesn't make sense is believing that every human being is always intelligent and rational and never forgets anything.
They'd be doing it because Shmaleksandr O'Kogan built a Google wrapper with a cool This Is Your Digital Life feature. After Cambridge Analytica, it's pretty hard to believe that user opt-in is an effective defense against data privacy scandals.
Apple should provide the option.