One of the banes of mobile game developers is the "fast food" culture of most mobile casual players. This not only means that they will download dozens, if not even hundreds of free games, try each one for 10 or 20 seconds and then delete it if they don't like it in that time, but it also means that many of them will easily give a 1-star (ie. minimum) rating on such games.
The 1-star ratings, and the ease by which casual players give them, are a bane of developers. Many (way too many) of them will give the lowest possible rating for the flimsiest of reasons, without giving the game, or its developers, any leniency or chance.
One of the worst possible things that can happen is if your game sometimes crashes on launch. You are pretty much certain to immediately get tons of 1-star ratings, right off the bat. (Of course it is genuinely bad if your app crashes on launch, but sometimes this just happens even with competent developers, for quite many reasons, some of them not even being entirely their own fault. Maybe a new version of the operating system breaks things, for example. You can see this all the time, even from really big-name developers and big-name apps. Heck, even Apple's own apps sometimes crash on launch, or during execution. Even they are not immune to this, even though they should know best how to develop apps for their own system.)
Of course that's not the only situation. Maybe your servers are momentarily down and the app can't connect and thus not function properly? 1-star ratings. Maybe somebody else's servers, which your app depends on, are down? 1-star ratings, for no fault of your own. Maybe they don't like your in-app-purchasing system (even though they are basically otherwise getting the game for free)? The list of reasons is plentiful.
The casual player masses are sometimes really "trigger happy" with their 1-star ratings, and will do it for the flimsiest of reasons. This can really drag down the ratings of a game, sometimes for no good reason.
And people, generally, trust these ratings too much. And low ratings will quickly drop the game down the list of thousands of other apps, and into complete obscurity.
It's a really harsh marketplace.