It only makes sense to use a single platform if that platform has proven to be more secure than the others. Neither Android nor iOS has proven to be inherently

It only makes sense to use a single platform if that platform has proven to be more secure than the others. Neither Android nor iOS has proven to be inherently more secure than the other (both have had plenty of in-the-wild exploits... the basis of most jailbreaking is due to such exploits). If neither platform is provably more secure, it makes more sense to allow both because in a fully homogeneous environment a single new exploit opens all the doors while in a mixed system environment, it only opens a subset of them.