Speaking as somebody who stayed on it way too long (until 10 years ago, maybe) it was because people constantly told me scare stories about how difficult it was to configure into something usable.

I had to go through the torturous path of Ubuntu -> Mint -> Mint Debian -> Debian. The last step was after I used a Debian live disk to do something and I could see that the stories were nonsense; just something that had adhered to the word Debian in my mind through repetition.

The two worst parts about it were 1) that I had long left Ubuntu on servers and had been using Debian there for years - I was just afraid of the desktop for some reason, and 2) that if I had just listened 15-20 years ago when people told me that FrankenDebians were nothing but problems, I would have never been caught in the net.

I've never been a fan of Ubuntu's business practices, but I'm just generally not into Debian derivatives anymore. If I were to leave Debian, it would be for an entirely different (and philosophically different) distro. I probably make an exception for Devuan, because it's only trying to change one thing (that I think of as the biggest threat to Linux, the final boss evil spawn of RedHat.) Devuan is an escape hatch for when the rugpull happens.