iPhone does not have a majority stake in the phone market anymore and they haven’t for over 5 years. So, I am not sure why you are saying they have the majority. However, I think what is much more likely is that the trakt team has some experience with iOS apps/devices (possibly form personal or past projects) and want to start with something they are more familiar with. Additionally, iOS is easier to build for because of the streamline of the software and hardware. There are only about 30-50 different hardware devices that run a version of iOS while there are hundreds (or thousands) of different hardware for Android and this inherently makes it harder to account for all variables.
Honestly, I am just excited that the trakt team is focusing on app development at all and am looking forward to the day I am invited for an alpha or beta (fingers crossed) for Android.