Here in the states we have a single lever. Supposedly if you give it a quick press you get a small flush and if you give it a longer press you get a larger flush. But what happens is that the lever never quite works that well and either always gives you a small flush or always gives you a large flush.
A single lever is cheaper to make than two buttons. A single lever thrown together with cheap materials is even cheaper.
In America you pay through the nose and get quality, or you get crap for cheap. There are fewer and fewer middle ground choices where you can get something that is well made for a decent price.