I have couple of small side projects that which are monetised through ads. Portfolio of those web apps are 7 years old and traffic is growing linearly. The problem is revenue, which is basically cutting in half every 12 - 18 months: both CTR and revenue is going down.

There are a lot of people with adblock these days, but also mobile traffic is not that profitable and people learned to ignore the ads as a noise. I am also using just one small rectangle per page and not going for more aggressive tactics.

During those 7 years I am down from "these apps are paying my rent" to "I can have a one meal in a nice restaurant each month".

The point is: it is getting much harder to make money by having ads in your app. Also make sure that all the information are recent and comes from your market sector as is changing real quick.