Debian 4 was when? 20 years ago, I suppose. I use Debian since then.
Haven't touch Windows since... 8? What was the version where they drastically changed the UI?
Why Debian? 20 years ago we had Red Hat (corpo-shmorpo something it was even then) and Debian. Plus some experimental heavy-maintenance demanding ones like Gentoo. I'm not a sysadmin, I just needed an OS to run programs. So Debian was the only option. Never had any reason to even think to move to another distro.