You list many valid grammar mistakes made by many people. In many cases, it comes from the elimination of teaching sentence diagramming. I learned diagramming in seventh grade and went on to teach it for most of my 34 year stretch as a teacher. Diagramming is as important to understanding grammar and sentence structure as dissection is to medical student education.

In addition, too many people believe that spell-check and grammar checkers are the ultimate authority on writing. This is just NOT true. If you spell a word correctly but it is not the correct word, some programs will not correct you.