It's not a local search. If you want a local search, do a local search. If you type a search into a global search box that is supposed to search the Internet, expect it to search the Internet!
It doesn't search the Internet. If it searched local files and Google (and maybe Amazon) it would make some sense, but (by default at least) it only searches local files and physical Amazon products, an absolutely bizarre grouping.
People are not used to a search area that looks up local AND internet resources. Furthermore, AFAIK, thre is no obvious "local only" search box to act as an alternative to this global one.
It's a combination of user expectations of a local search resource and the lack of obvious warnings about this new, and odd, feature.
> People are not used to a search area that looks up local AND internet resources.
This is the crux of the matter. I would argue that they are used to this. Ordinary users aren't aware where they are conducting a search at all. They just expect the computer to figure out and do what they mean. The distinction between the Internet and local storage is already being lost on them (examples: Dropbox, Google Drive). The fact that so many users put URLs in a Google search box is a perfect example of this phenomenon.
The set of users who do understand the difference are capable of directing their computer more specifically. The default does not matter for them.
Ubuntu is supposed to be usable by everyone. This is (I assume) why the default is the way round that it is.
> the lack of obvious warnings
Have you looked? There is a warning on the same screen as the box, complete with a link to a privacy policy. Or are you saying that this isn't enough?
