Because they don't compete with each other? They are in different markets and they don't really care that a portion of users stick to Apple. I'd say the opposi

Because they don't compete with each other? They are in different markets and they don't really care that a portion of users stick to Apple. I'd say the opposite, having Android with a 90% market share would be a bad thing for Google since it opens easier antitrust lawsuits. The statu quo is more profitable. See the "Our vision is that we work as if we are one company" quote from Google execs which is representative of what's happening in the space.