Email began with people generally writing without paying much attention to how they write. Even punctuation went out the window many times. Form was ignored.
Texting is even worse. The words became shorthand, and again punctuation was slaughtered.
The young generation today grew up reading and writing electronically. The electronic communication form is now their primary form. Instead of writing long letters with style and flair, they condense and use icons.
IMO this grammar, spelling and form decline is a direct product of that, along with the lack of reading.
I see it everywhere.
I was guilty of it myself when I first began writing emails. Early on, a wise friend told me I should treat an email just like a business, or personal written letter because otherwise I will get lazy. He was so right! Even doing that I still find myself falling into the lazy mode of popular electronic communication.
Going to the point brought up by the OP, "would of" or "woulda, coulda, shoulda" - if written in a purposeful dialect style is correct in form. But so many times it is written out of ignorance. That is a very sad realization of the lack of the knowladge for proper English people have become conditioned to believing.
Living in the SE US I hear butchered English spoken constantly. Speaking it is showing a lack of understanding but sometimes acceptable due to a colorful way of speaking. I adore hearing a colorful speaker, with wonderful stories. But writing it, without a clear understanding of the audience that it is only a dialect being used for a purpose in the written piece, shows a horrific lack of education.
When I hear a Mom that home schools her kids consistently say things such as "She done it" makes me fear she is teaching the children the same grammar in her school setting.
It's sad.
