Why can't IE be released in a form that is not so tied to the OS, and leave the old IE bits where they lie? In XP, for example, they could leave the rotting old

Why can't IE be released in a form that is not so tied to the OS, and leave the old IE bits where they lie? In XP, for example, they could leave the rotting old IE8 guts in, and release a standalone IE11 that opens instead of IE8. Of course, I would much rather they just exit the browser market entirely. They keep embarrassing themselves over and over again. While new releases are (finally) somewhat modern, there are still incredibly frustrating new bugs with every release that take years to get fixed, holding the web back again and again.