You will see many firms make an attempt at two platforms or try to exploit some dev into doing two platforms at 100 hours per week keeping up. Here are the numbers of why they do crazy stuff like that.
The normal or average conversion rate to MAU is 30%.
Android market share of 80% means 24%
iOS market share of almost 20% means 6%
Obviously, some firms are not yet waking up to the numbers and that generally is due to what resources they may have already deployed towards covering 2 mobile platforms.
If you are a new start-up than obviously you might to re-think the mobile platform choice.