Oral language is constantly evolving, while written forms don't change. That makes a gap between spoken and oral forms, you tend to speak a bit different from our parents and grandparents. After generations language can experience a big difference between written and oral forms.
However, both Spanish and Italian have constantly been revised throughout history, in order to match as best as possible the spoken to the written form. English, on the contrary, has evolved in a much more free way and it has just been a matter of time to separate that much.