I think the difference between Microsoft and Apple is that Microsoft is an enterprise company who dabbles in consumer things while Apple is a consumer company who has zero interest in workspace/enterprise stuff. The real threat to Microsoft is Google as they are the ones actively trying to undermine Windows/Office and to a lesser extent Active Directory. Apple does not give a shit about the enterprise and only focuses on consumer products for the most part. This allows them to be pretty nimble as they are structured around essentially one to two major products at a time. Microsoft on the other hand has a serious problem as their internal culture crushes innovation, promotes career posturing antics and is ridiculously middle management heavy. They know that they can shit out crappy versions of Windows until the end of time though, there is nothing else in the enterprise space to dislodge them. Consumer Windows is far less important and Apple still hasn't made a serious dent in that.
The Xbox is their only real success in the consumer market these days and even that is more of a result of throwing money at the market until it stuck. They still face two large competitors and now a public with heavily divided attention spans due to the ever increasing number of ways we get our entertainment.