Because you can’t tell someone has a male or female brain until they die and you cut them up.
People in that situation will show their gender reassignment certificate. It’s actually not that complicated. Uncomfortable, sometimes, but complicated, no.
I have never. In the distant past, probably somewhere around 100 BC or so, I produced a college transcript when applying for an internship during a summer semester. I still have my physical degrees, but they are gathering dust rather than sitting in my briefcase ready to be shown to all and sundry.
Pretty sure that when you’re proving you earned some degree, you don’t hand over your diploma, regardless. It’s going to be some kind of transcript or letter from the school, and I wouldn’t be surprised if those records are ones you can have your name changed in (and gender, if included).
It probably would take nothing more than a visit to the Registrar’s Office with your legal paperwork in hand. People change their names all the time and there has to be a procedure in place so that academic records can stay linked with people.
They might not re-issue the actual physical diploma, or allow you to “walk” in cap and gown again and be addressed with your “new” identity, but the paperwork should link up somehow.
My alma mater, at least at one time, had simple certification forms (1 8.5x11 Letter sheet) that stated your name and degree(s) issued by the school. E.g. “John David Smith, BA English, 1995, JD Law, 1999”, if all you needed was proof that you had a degree. I would suspect that they would issue that under your current legal name if you provide proof of name change. Of course, the standard transcripts were available as well.
My mother went back to school after she got married and all her old transcripts were recorded under her maiden name - she didn’t have to go back and retake all her classes under her married name - they accepted the old transcripts. I don’t know if she amended the records or just provided a copy of the old transcripts and a copy of her marriage certificate to the grad school admissions department, but it worked out.
The Virginia DMV had me submit medical reports to the state medical authority every so often for nearly 4 years after they gave me the F. Finally they decided they were satisfied, closed my case out, and have since left me alone.
By the way, as for making you get divorced, they didn’t even ask whether I was married, let alone care.
Leaving aside the problem of the phrasing “biological female” another important change is that testosterone will irreversibly enlarge the clitoris, often to the point where its extremely prominent and microphallus-like in appearance.