Android devices come in all shapes and sizes, with vastly different performance levels and screen sizes. Furthermore, there are many different versions of Android that are concurrently active at any one time, adding another level of fragmentation. What this means is that developing apps that work across the whole range of Android devices can be extremely challenging and time-consuming.
The screen size fragmentation can eventually be dealt with yet it’s the adoption that kill all the fun (1.5 years for Android 4 to get to 50% aye?). And as we all know: it’s the lowest version that’s always holding things back.