Why are there so many different referencing styles?

Because different disciplines need different information foregrounded, and each developed conventions that suit how it actually reads and uses sources.

The main families:

Author-date systems (Harvard, APA, Chicago author-date) put the author's surname and year in the text: (Smith, 2019). The year is prominent, which matters enormously in sciences and social sciences where the recency of a finding is central to judging it. APA is standard in psychology and education; Harvard is a family of similar styles rather than one fixed standard, which is why university Harvard guides differ from each other.

Numeric systems (Vancouver, IEEE, Nature) use a number in the text pointing to a numbered list [1]. They are compact and unobtrusive, which suits medicine and engineering where papers may cite a hundred sources and inline names would overwhelm the text.

Note systems (Chicago notes-bibliography, OSCOLA, MHRA) use footnotes or endnotes. These allow discursive commentary alongside the citation — a qualification, a counter-source, an aside — which is why they dominate in history, law and the humanities, where the note is often part of the argument rather than mere bookkeeping. OSCOLA exists specifically because legal citation must handle cases, statutes and jurisdictions that generic styles cannot.

MLA, used in literature and languages, emphasises the page location within a work, because close textual analysis needs it.

What all of them are actually for, and the reason the details matter less than students think:

Attribution — giving credit and avoiding plagiarism.

Verification — letting a reader find your exact source and check it.

Signalling — showing what your argument rests on.

Practical advice: use whichever style your department requires and be consistent; use a reference manager rather than formatting by hand; and always check its output, since managers import bad metadata routinely.