Why do we need to use abbeviations from Greek or Latin?
We don't use Greek abbreviations. Greek words are written in the Greek alphabet. Most people can't read or write it any more, and even if they could it's a hassle to reconfigure your keyboard.
Latin was the first language to be written in the Latin alphabet (duh!) so the monks who were doing all the writing developed abbreviations for common scholarly expressions as a way of making their jobs easier. Before the invention of the printing press most people had no need to be able to read and write, so it was all up to the monks and government officials.
When the Roman Empire collapsed, Latin continued to be the language of scholarship so scholars kept using those abbreviations. When the printing press was invented, people who never learned Latin learned to read and write, so a significant amount of material began to be printed in other languages. But by then the old abbreviations had been so thoroughly established for 1500 years, that scholars kept using them and so did printers. Nobody bothered inventing abbreviations for the equivalent terms in their national languages.
Today we have a choice, and many English phrases have replaced the Latin ones, or at least stand side by side. We can say "and so forth" instead of
et cetera, "in other words" instead of
id est, "for example" instead of
exempla gratia, "and others" instead of
et alii. But we have still never bothered to invent abbreviations for those terms. We still write
etc., i.e., e.g., and
et al. "Et cetera" is so well known that we actually read it in Latin, but hardly anybody knows what the others stand for, so we usually translate them into English when we say them out loud.
In writing you're free to use "for example" and "and so forth" instead of the Latin abbreviations, and many writers do. But there are still no abbreviations for them in English. You have to write the whole words out.
That's why we use the Latin abbreviations. It's easier than writing the words out.
Of course if you speak German you've got it made. They compulsively translate practically
everything into German. Instead of
etc., Germans write
usw for
und so weiter.
