Who is to blame for adult illiteracy?

There are many things I come across during the course of an average day or week, but one thing that troubles me greatly whenever I’m faced with it, is adults who struggle to write. When I say struggle I mean that they can barely form letters, or words,and are therefore unable to write a coherent sentence.
I can’t really imagine what that must be like for them, but the closest I can get to it would be me trying to write in a foreign language.
I'm not talking about Dyslexia or the odd spelling mistake - I'm talking about being illiterate.

At present about 1 in 5 adults would struggle to read their child a bedtime story out loud.

I can understand this situation if the person/s has come from abroad and didn’t have the opportunity to go to school, for economic or cultural reasons. I can also understand it for those who have suffered ill health and were unable to attend school. I can also 'kind of' understand it for those from very troubled backgrounds, yet still…when I come across someone who was born and raised right here in the UK, and went to school here in London and left that school unable to write, what on earth is that about?... I struggle with that.

I feel deeply compassionate towards these people, and quite curious about our education system

Imagine..
Struggling to write your own name
Filling in forms
Not being able to read the paper
Never writing a love letter
Filling in an application form
Completing benefit forms
At work
Finding a partner
Passing your driving test
Getting lost and needing to read street signs - road names
Instructions
Letters
The list goes on...

Who is to blame?
And if we’re in agreement that not being able to read isn’t the fault of the individual, is it direct discrimination to expect people to fill in application forms for jobs?

I’ve got a lot of respect for adults who take that bold step to learn to read in their adult life...on so many levels, it can’t be easy. The hardest possibly being dealing with the fear of peoples reactions.
When you consider the benefits however, it's worth ever moment of that short lived discomfort.