If it's compulsory, it's by definition not a choice. It's not taking an option, a slot, a 'choice' for another GCSE.
It takes time to teach and has to be taught in some form, even if not as a GCSE. So that time would never be allocated to a different subject. Gaining a qualification is at least some recognition in addition to the skills achieved.
You could argue the same about something like English Literature. It's not core, functional English, but most schools teach it alongside Language. It takes up what could be an extra GCSE in another subject and can be aligned with other humanities subjects (which usually aren't all compulsory, even if one has to be selected for the school's results 'bucket') as much as English, but people don't complain or try to remove it.
I doubt the chance exists within the timetable (as in both there won't be enough hours left to cover another GCSE, and there won't be the staffing/rooming to offer something additional at that time) for anything else.
In some schools, as an example, pupils can choose triple science, and because of how it's timetabled, then can't physically then accommodate a language and a technology, forcing two of just one subject type.