~30,000 downloads and only $150 a month? That's a horrible ad revenue
It depends on the game. AD revenue doesn't fit every game. 30.000 downloads with maybe 1$ per CPM would still only be just $30 if all those players saw an AD on average 5 times. Sounds about right.
ADs is a terrible monetization choice unless your game has a long life. Fit's well on games that has a long life time, like candycrush, angrybirds etc, where you expect people play daily, for a long time. If you're making a game that you can finish in an hour / couple of hours, then never play again, AD's is the lousiest way to earn money. It doesn't matter if your game has 1 Million downloads you will never earn a lot if the player only sees a couple of ads during the whole playthrough, then uninstall.
I think many devs think Free with Ads fits every game, and they can get a lot of downloads and earn a lot of money, but it all depends on the game. You have to design your game around the monetization model to have them coming back and play over and over, otherwize Ad's is useless.
Or let's turn it around.... Let's say you earn $1 per CPM, that means ONE player has to see 1000 ads in order for you to earn $1 from that player. If your game is fun enough and the player sees on average maybe 10 ads every time he plays. He has to play your game 100 times, for you to earn one lousy dollar from this player.
I think the reason many games don't earn a lot is because the choose the wrong way to earn money for their games. Ad's can be very lucrative if you're game is a hit, and your game is designed for people to play daily. But if not, choose different monitization models. IAP's or just simply sell your game for 99cent would earn you way more than AD's if your game is short, and you don't expect your player to play your game during a long period.