Trt - Because 'text speak' is a childish form of communication. When kids get together, they invent new words for everyday objects or situations. I did it when I was young and speaking to my friends and colleagues, they did it too. When email (and mobile phones) first came along, kids used phrases like 'LOL' and 'IMHO' not only as an expedient way to express an emotion without going into elaborate exposition but also in order to create a 'new' language that couldn't easily be deciphered by those non-initiates.
'LOL', 'IMHO' and even 'ROTFLMAO' are phrases that I fully understand (I was joking when I said I had to use google to find out its meaning) but I consider them to be a rather crude form of communication.