I wonder how much of this is due to spellcheck being prevalent in our lives, but grammar checking software being less so.
If a person types something and no squiggly lines appear, the user is given false confidence that the written material is fine.
For example, I spent many years working in a corporate environment in the Tampa area. Various promtions were run to incentivize the sales staff. Sometimes this would be a pair of tickets to see one of the local pro sports teams play. Far too often when a flyer was printed or an email sent out for tickets to the Tampa hockey team, it would refer to the Tampa Bay Lightening, rather than the Lightning. The spellcheck software at that time assumed the user was trying to say the opposite of heavy, rather than the weather occurence that causes thunder.