A lot of tech illiterate users don't even know that there are multiple search engines or that you can change the default one. Being the default is highly critical there.

yes, but a vast number of users tend to stick with the defaults.

Until the default changes and those of us who don't like change will learn to make the effort to revert back.

I have no idea if google is actually a better search engine, just that it's a familiar one.

For most searches the average person does - aka I want to go to the wikipedia page or official site for X - the results are indistinguishable.

That's not a good measuring stick. Probably even before Google existed search engines we're good at those kinds of searches. But people use search for much more than that.

On iOS — in contrast to Android — you can actually change the default search provider, yes.

(On Android you can't change it at all. And so I'm either stuck with a Google search on the Recents menu, or the "this widget could not be found" message)

If you're talking about within the Chrome app on Android then, unless something changed in Marshmallow, you can totally change the default search provider. Chrome > Menu > Settings > Search Engine allows you to change the default search engine in the browser, but you can't add new ones to their list, so it is a limited set of options available.

If you're talking about at the Google Now or Siri then as far as I know that's not possible on either OS.

The one I find most annoying on Android is the search bar on the home screen. Even though you can customize most of the rest of the screen, you can't change the search provider for that bar, or even just remove the bar. At least, not without replacing the launcher entirely, with something like Nova Launcher (http://novalauncher.com/), which is what I eventually did.

This is not really an android flaw but a nexus one, because its default launcher is part of the google search app. On many android phones, the search box is a widget that can be swapped out with a widget from any other search provider or removed entirely.

But this bar also appears on the "Recent Apps" menu, and can’t be changed there, at all.

You only get either the bar, or an error message, which says the Google App can not be found.

I am talking about the Google Search bar in the Recent Apps menu on Android.

It’s at the top since 5.0, can’t be removed, can’t be changed.

If you root and disable the Google App (yes, you now need root for that), then it is replaced with an error message, saying that the Google App could not be found.

There is no way to replace it with a search bar for bing, or remove it.

you can change the default search provider in siri

Yes, the default engines in Mobile Safari are Google, Bing, Yahoo and Duck Duck Go.