This is a huge reason. Also the physics engine, which feels very smooth and intuitive.
Those trajectory style games are as old as the hills. Didn’t seem significantly different to hold my attention for more than a few goes.
I heard about it on some website for ipad apps, tried the free version and then bought it. I think the appealing thing is you can do it quickly. Have a few minutes of coffee break time left at work?
Pull out the magical ipad a stage and start flinging birds and triangles and bombs (love the bombs). As others have said, it is fun to throw things and see what scatters to where, like ripples in a pond when you throw a stone or a daisy or a little girl (“Frankenstein” joke. Of course little girls are not for throwing into water).
That’s just like, your opinion, man.
There are a few reasons:
It is very simple.
The graphics are colorful and have a lot of personality
It plays to the strengths of its platform (i.e. touch screens)
It has a great deal of that “Just one more try” addictiveness.
Sometimes once something reaches a critical mass of popularity, its popularity becomes self-sustaining. I think Angry Birds has reached this.