Because this can be a form of brokenness. Someone would be hired for their aptitude and probably not because of something they have already repeated over and over (unless we include factory work). The ability to adapt and create (and be creative) is usually not described as such in SWE work, but a lot of the actual work does include that.

That said, if a job has a match based on OS, it would probably just as much be a good thing to explicitly know that you either will be or won't be a good fit based on what you are used to and what you think you can adapt to. Knowing this about a job or a potential hire saves everyone a lot of time.