I’m gonna throw some feedback out on the other side of the coin here, because I think there’s an alternative perspective to be had.
My background in gaming is almost strictly on PC. I’ve had consoles over the years, and more recently phones, that I play a few games on, but I almost exclusively game on PC. To that end, the option to exit the game is something that’s ingrained in me. During the development/release process of my mobile game, CodeLogic, I discovered that there’s a bit of a perspective shift that occurs on mobile… and indeed, between different mobile platforms.
So first off, games on mobile (and console, for that matter), aren’t actually expected to have an exit game option. In the case of consoles, they run until the user turns them off in some way… for classic consoles, this was just a power off. For modern consoles this is a task switch. For mobile, applications (not just games) are really expected to just be there and the operating system handles task switching. When you’re done with the game, just hit the home button (or whatever) and it will suspend. The expectation is that it will resume (in some form or another) when the user goes back to it.
There’s a bunch of different reasons for this but at the end of the day, apparently it comes down to battery usage. I did some googling a while back, but apparently from the mobile OS perspective, it’s more efficient to suspend a task than it is to entirely load it again later. Some folks jive with this, some don’t. My phone generally has only 4-5 “open” apps at any given time, but my girlfriend’s has like 40+. I’m used to PC where I have this obsessive need to manage my resources, she doesn’t give a crap and just does whatever. Both of us have an equally fine usage experience.
Something else to note here… there’s also a different expectation on user base. I’m primarily an Apple user. I don’t really care but it just so happens that I ended up with an Apple device when I first started using a smart phone and, well, here we are. So when I built CodeLogic, I did so from the Apple perspective of app management (ie, fully embrace task switch, don’t expect users to want to kill the app). Of course, Apple is dumb if you’re a small independent dev with no cash flow, so developing and releasing on iPhone was out of the realm of possibility. Instead, because all the tools are free, I developed using Android as my primary target and had a group of friends be my testers.
From a few of them, one of the strong pieces of feedback is that they wanted the back button to do something and, ultimately, they wanted the back button to allow the app to kill the app from the main menu. Easily 90% of my test group didn’t care, but 10% felt pretty strongly. Ultimately I did hook this up because everybody liked the back button functionality and, once I had that, hooking up a task kill was trivial.
Anyway, the moral of this long-winded story? I don’t think it’s actually bad in any way for a game to not have a way to exit, depending on the target platform. If you’re targeting PC, yea, you need a way to exit. If you’re targeting mobile or console, it actually doesn’t really make sense to do so… a very small fraction of your user base is even going to look for that functionality, let alone care. People will just task switch away and forget about it until they want to play again. This is apparently the new normal that only those of us with PC gaming backgrounds find weird.
Anyway, hopefully that provided some additional perspective! Best of luck 
