Advertisers pay more to appear in games which audience is for them more relevant, more likely to join their game.
I experience a bitter demonstration of that right now and here are my two extrem cases.

Weekly Admob banner numbers:

As you see creepy has around 13x times more impressions by players, is generally played more and longer.
But it only made $1.28 and Brofist Legend $4.01.

If Creepy would have the rpm of Brofist it would have made 51,40 this week.

I wonder if there is any chance to increase the rpm of a game retroactive.
But I am afraid its just depending on your theme and keywords.

But overall I am simply happy that we have that extra monetization channel now specially since Android games had no such option before. Its not gigantic but still noticeable and helps me definitely paying my bills. So thanks game salad for adding it.

I learned something so I shared it here,
Cheerio Dave