Why can't graphic designers see spelling mistakes?

 Not sure if this is a generalization, but quite a few designers I have worked with have difficulties with English spelling. I have often thought that they are so visual that they have never bothered with getting spelling right at any point in their career. Also doesnt help that most design software doesnt exactly do spellchecks. 

But I was reminded of it when yet another designer I was working with made quite a few basic spelling errors. 

Strengths and weaknesses, plus these are strengths they hone so well and are used to someone else always come around and correct the spellings!