[cuddlybacon]

Tom Scott has a nice intro video about this: https://www.youtube.com/watch?v=fS4X1JfX6_Q

The book he mentions, Because Internet, goes into more detail. But to over-simplify, there were a few major generations of people joining the internet as well as a generation that never fully joined, and each one developed its own conventions for casual writing on their own. Some used the same mechanism to mean different things.