Erm...because it's incredibly annoying?
If you're using a a device ill-suited to communicating in written language (mobile), txt speak makes sense, insamuch as it's possible to make sense trying to use a voice device for text messaging.
On this forum, with a keyboard in front of you, it makes no sense to use txt speak, must take more effort to type that way, and certainly takes a lot more effort to understand.
a little hypocritical don't you think if others are going to be picky then so will i
No that's just you again. It's an accepted exception, by definition it's "txt" speak.