I cannot comment on developers' preferences as a whole, but I personally have several large floaters (https://en.wikipedia.org/wiki/Floater) and using a display with a bright background makes them very noticeable and distracting. Which is why I use Dark Reader (https://chrome.google.com/webstore/detail/eimadpbcbfnmbkopoo...) for websites and dark themes in my OS/terminal/IDEs. It's not just an aesthetic choice.