I would imagine the the market for utility apps is a lot less competitive. Also, developing a game would take a lot more time.
The upside to games, is there are all kinds of knock-off apps you can purchase cheaply. Also, you can generally hire devs to quickly knock off a well-known game. So there is something to them.
The flip side is, even when that strategy works, the life span of games tends to be short. Unless you've got a legit Clash of Clans on your hands, it's a get in, hit it hard with ads, and get out. So game clones is a reasonable market to do small numbers.
But ads don't work unless you have eyeballs. And that means engagement and continued game play. And most games just don't have that kind of stickiness.
It used to be that I could just focus on getting an install on the device (and games worked well for that). Then I could put AirPush or StartApp in there and make money whether the user was engaged in my app, or not.
But those days are pretty much over. Google's pushing app developers to a space where if the user isn't actively engaged with your app, you're not going to be able to monetize it. Apple's been in that space from day 1.
So now it's more important than ever to have an app that can be monetized, even with limited engagement. For me, that means utility apps as opposed to games. And it also means I've largely removed ads in my apps. I can make so much more by having smart placement of in-app purchases, and cross-promotion for other apps of mine.
That's just my opinion... but it does seem to me like most people trying to go the games w/ advertising route are probably trying to make an outdated model work. Google killed that pretty dead at the end of last year.
*Note* That doesn't mean it won't work. Everything works to some extent. There are still people killing it using that method. My friend still brings in $20k+ each month using that model... but he's also got 5,000,000+ installs working for him. It's just that it's a harder game to play today than a year ago. It's not where I would start, and it's not where I would focus my resources.