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.
Eh, it’s just shifting of how written work is relfective our spoken word. It’s pretty rare for me to use a stronger “ah” sound when saying “would have” most of the time defaulting to a softer schwa sound, which sounds almost exactly how how “of” sounds. English has been changing and evolving for centuries. There’s even major epochs like the great vowel shift. Hell if Shakespeare were around today and making the drastic changes to the english language like he did back then he’d be crucified by internet prescriptivists for using English improperly.
If you’d like something a bit more modern, Mark Twain broke english rules all the time in his writings and he’s considered one of, if not, the greatest American writers.
I’m sorry but it doesn’t fully work here. ‘of’ phonetically should not be spelled with a ‘f’, so they are already using a word that is not pronounced as it is written, might as well use “would’ve”, which removes the part that isn’t pronounced as it was traditionally “ha-”, but at least it’s still correct.
They use ‘of’ because they don’t understand (or pay attention to) the grammar of what they’re saying.
Shakespeare did not “make” changes, he’s just a very good record of changes that had taken place.