…the reason “in some dialects of English native speakers really do say ‘should of’ etc” is phonetics. Kids hear “should’ve” and repeat it phonetically, before learning the actual words or their meaning. Combine that with the awful state of education and literacy in the USA (and other countries etc) and voila, you’ve got some armchair internet expert justifying it with some big words trying a weeeee bit too hard to make it work.
Then you’ve got teachers who still gaf and know their shit who will correct this before middle/high school, and no, last I checked it was never added to the dictionary or considered correct. Language of course is living and ever changing, but the line must be drawn somewhere lest we devolve into shouting and grunts like neanderthals