Why YSK?
The first person who typed “should of” probably heard of it in real life that was meant to be “should’ve”, they typed “should of” online and readers thought that it’s grammatically correct to say “should of” which is in fact wrong and it became widespread throughout the years on Reddit.
I hope something could start to change.
In Canada - we will’ve stolen it from Ireland or Scotland - we’ll jam three contractions onto the end of a word. I forget which case it is, but I run across or write it almost weekly. It’s like a “will have been” kind of super compound phrase.