My main reason is that Debian is a very stable, very popular distro, that isn’t a fork of another distro. The fact that it’s stable means issues are more rare; the fact that it’s popular means when issues do pop up, there are much higher odds that I’ll find others who ran into them before; and the fact that it isn’t a fork means that I can just prefix “debian” to any search, rather than say having to contend with it being potentially a “debian” issue, or an “ubuntu” issue, or a “mint” issue. In fact, debian is popular enough that most of the time I could just prefix “linux” to a search, rather than “debian”.
While there are distros that market themselves on other merits, it seems to me that the main goal of an operating system is to be a stable foundation. I wanted to pick something that would let me have a good time with i3; Debian seems one of the most straightforward choices. I considered arch, but in the end Debian seems like the lower-effort option.