Well as to why they were chosen back in the STS (shuttle) era (before my time) see a good history on the decision here: https://forum.nasaspaceflight.com/index.php?topic=27043.0

1. In the space program decisions are made years before and changes are very difficult owing to a myriad of reasons from procedures to paperwork, eg there was a whole mirror lab setup on the ground To support them etc

2. Astronauts/Aerospace operationally often come from defense world - they are used to windows - see DoD -that battle was fought in the 80s/90s

3. Once something is a part of the space program it takes on a life of its own/ we had an IIS webserver onboard the ISS for example and also apache tomcat - we (myself wrote software for both) using .NET and Java

4. Training and operational software and docs were all MS Office variety for years (were talking from floppy disk era here)

5. Lot of other linux/unix based systems too this is is just crew support laptops - not considered mission critical