People do pick based on career (not sure about UK specifically but generally sperm recipients can see that kind of biographical info), but it’s not like nutting in a cup is difficult, and someone might want sperm and not care what career the donor has. Why not just donate in case if someone wants it?

I’m not sure how long sperm lasts, but when I was doing egg retrieval I was told that frozen eggs can last at least 10 years, probably a lot longer but they only store them for 10 years as they have limited space. If sperm is similar then there’s a decent enough chance someone will want to use it.