Hm, almost every desktop program i have on Windows that bothers with help uses CHM and pretty much every documentation generator can generate CHM files, why do you think it isn't used?
Try to find node, go, vscode etc ... documentation in chm. They have third parties versions sure, but not official. And for those that still uses it, it’s rarely up to date.
Of those only VSCode is a desktop application and VSCode is already a web browser. Also considering it is meant to be modular, its documentation system would also need to be modular and i'm not sure if CHM is good with that.