Not really sure if you're talking about Budgie, GNOME, MATE, or Plasma here, but the concept of search providers in Budgie isn't a thing. This might be something that gets explored in the future once I make some more concrete architectural changes to search, but simply isn't a priority. Personally I find search providers in GNOME Shell to be pretty limited in usefulness. File searches end up pulling from Tracker, which is a bloated pile of garbage that only serves to waste computing resources (CPU, storage, etc.). Most web based searches are...well done in a web browser that you're likely to have open anyways. Mathematical calculations are questionable at best, anything complex would warrant features you probably wouldn't expose in the menu itself. Really the focus of the menu is always going to be applications, everything else would be secondary and likely be a deferred search operation, at which point the search for it would be slower and already be less useful than opening up a dedicated app for it (like a file manager, calculator, browser, etc.)
Generally speaking implementing an package search provider just isn't a meaningful use of time either. We have a Software Center that can provide a much more curated experience than what a search provider could, and if we were talking about GNOME Shell then we'd have to constantly update it against newer GNOME Shell releases. Doing this across multiple desktops? Pretty much forget about it. Building a package manager oriented search provider on top of eopkg / pisi wouldn't be useful either, since it'd have to be rewritten for sol anyways.
So it's a good suggestion and I can see where you're coming from, I just don't see it being especially useful or a priority and there are better places (Software Center) to provide an improved experience for package searching.
