[susan53]

Do you mean why is there no one standard English? For the same reason that there is no one variety of any language unless it's spoken only in a tiny and socially cohesive geographical area. Language is not "fixed" - it changes constantly as people adapt it to their communicative needs. And if people live in different areas, then changes that happen in one area may not happen in another - hence the differences between eg American, Australian and British English. Just as the birds in different areas evolve differently due to lack of contact, so does language. With the closer contact we now have due to globalisation, the internet etc, there is currently more overlap than before - most American English is now understood by Brits and vice-versa - which wasn't always true when I was a child, before TV programmes were exchanged across the Atlantic and when ordinary people didn't travel abroad. (Yes, I'm that old ....) But with the developing role of English as an international language - and not just for international contact but also as a lingua franca/governmental language within countries which are not English speaking - more varieies are springing up. I read yesterday for example that in Hong Kong (or perhaps Singapore? Can't remember) a high-flying bureaucrat is known as an "astronaut". That's a purely regional usage, clearly adopted to meet the needs of the what the local population want to use English to talk about. As I said a few posts ago, if English didn't change constantly, we'd all still be speaking like Chaucer, and changes inevitably start in one place, maybe catch on maybe not, may remain local rather than general, or may spread to influence the whole language. Watch yourself carefully, and you'll find even your own use of the language (technically known as an idiolect) changing. I even caught myself saying something was "cool" the other day ...