I have a low RPM?

Hi,

I started making simple wallpapers apps, the RPM is around 0,7 to 1,2 $. Then I decided to make a better app, more complete, an app about photo frames, stickers on photos and many more functions…The app is much more better, but the RPM of this app is lower, around 0,1 to 0,3 $
I am using admob with banner and intesrtitial ads in both apps.
I dont understand why there is so much difference on the RPM of those apps, and why the better app has lower RPM.

What is an avarage RPM? I only made this two differents apps and dont know if the first one is very hight and the second is normal RPM or if the first app RPM is normal and the second one is too low…

What do you think I could do to improve it?

I am thinking to try other monetization system, what do you recomend? AppBrain?

Thank you!!