These abbreviations came about in the days prior to the internet. Then we had local bulletin board services (BBS) that were all alpha numeric and no graphics. There were information pages, posting sites and chat rooms. The chat rooms were by far the most popular and it was not unusual to have a dozen or more participants on line at one time. The conversation would move so fast it was difficult to read and keep up sometimes. At these times the best you could do was 1 or 2 line messages or you would miss half of the conversation or the conversation would move past your reply. You also had to be a fast and accurate typist. The abbreviations were so that you could get your say in and not get behind or lost in it''s meaning. We have come so far in such a short time!
The first time I saw TIA at the end of a message, I thought it was her name, Tia!