In public expression, we try to adhere as closely to Written Standard English as we comfortably can, as a cultural marker that we have been taught to care about standards, or traditions, or literature. How we write and speak declares something about who we are and what we value.
This has been changing under our feet for decades, and has been accelerating on the internet. Not only are forms changing, such as the increasing use of phrase-abbreviations such as IMHO, BTW, LOL, and WTF, but switching between Standard and Colloquial is increasingly valued in communication.
Hispanics who grow up in America switch back and forth between English and Spanish. Linguists call it code-switching. It is a declaration of relative comfort with both languages, and the rules of when to switch are not arbitrary. Black writers switch back and forth between Written Standard and African-American Vernacular, to make the statement that they have command of both and move in both worlds. In less dramatic fashion, writers like Dave Barry code-switch between colloquial and standard for comic effect. The use of sentence fragments is increasing in standard written discourse.
I should deplore this, but I like it. How someone who never splits an infinitve and will have to have the Princeton/Oxford comma pulled from my cold, dead fingers can countenance such solecism may seem impossible. But I still like it. So there.