A significant design obstacle with almost all search engines is that it's not entirely clear what you can do with them. They're just a search box, after all. You need either external training or a trial-and-error loop to figure out what you can do with them. This also means that if you change how they work, users get confused because their queries no longer give them what they expect (this is likely a big contributor to the "google is broken"-sentiment that's been going around).
This becomes a problem when the search engine caters to too many modalities of search, as there's an element of guesswork what the user want. Two users may even enter the same query, but look for different results. If I enter the name of a video game, do I want to buy it, or do I want information about it, or maybe fanfiction or something other than the game that shares the same name? Who the heck knows.