Well, technically, they didn't really steal. They just "got inspired by what they saw", I guess.
Then again, I use Linux, and it copies a lot of the good stuff from both Mac OS and Windows, and then adds some more. That just makes the product better. However, in Microsoft's case, they have copied a lot of Mac OS without adding a lot of their own, innovative, features, while preserving all Windows' downsides, that Mac OS just is a better product now ;-)
However, you need to buy new hardware for that, if you have a PC, so most people probably won't switch from Windows. And since they also consider installing an operating system too scary, they won't switch to Linux either ;-)