Debian is a large, complex operating system, and a huge open source project. It’s thirty years old now. To many people, some of its aspects are weird. Most such things have a good reason, but it can be hard to find out what it is. This is an attempt to answer some such questions, without being a detailed history of the project.
Because it's stable. Not some poorly bundled OS that has broken installers on their website for weeks like Ubuntu does sometimes.