This monotony is very easy to explain if we think of reasons making people play mobile games. These reasons are boredom and tiredness. People sit at boring lectures, or in the subway, and they get a desire to play some nice mobile game just to kill time. But mobile software developers shouldn’t forget that users are already tired – and shouldn’t force them to become more tired from a small mobile game. A monotonous gameplay makes a user feel comfortable: once adapted, he feels "like a duck to water." So, develop an interesting gameplay originally and don’t overload it further.

A small tip how to create an involving gameplay: make funny physics. I've recently played "Shark Dash" and couldn't just stop because of amazing game mechanics, all these pipes and bath sponges affecting movements of a small shark. However, using special physics in a mobile game is a proven way to make it successful since Angry Birds.

Use the most basic game mechanics such as matching, seeking, hitting, chaining items and some others; they can also be combined with each other.

2. Simple movements
In the most top casual games user makes only one move (touch) on the screen: a slide (Angry Birds, Shark Dash), a simple tap (Ninja Jump), or a slide (Fruit Ninja). Mobile software developers made it in order to simplify the gameplay and to make the game not depending on different kinds of smart phones whether they have physical buttons or not. Essentially, the whole game control is reduced to a periodic touching (or not touching) the screen and waiting for the outcome. After you’ve made your move, you just watch the situation on the screen, like in Angry Birds. You shot a catapult at evil pigs and just observe how birds are crushing everything on their way.

Let’s make a small break ;) Next time we’ll talk about such important elements of mobile game development as graphics, music and sounds. 

P.S. You can read more about mobile apps development.