But why would they illegalize access to a PC?
What do you mean?
There is no problem to use PC, but there is a limitation of internet usage. You need a special license if you wish to use internet, and only legal entity or government official are able to receive it. However, they have own national network... The most of sites in the internal DPRK network are providing technical documentation, textbooks, music, etc. If you need some specific information then you can send official request to upload a copy of specified site into national network... It usually takes some time to check the content, of course.
China and North-Korea is just 1 big pile of mess, which needs to be put to order.
Just try to imagine, somebody breaks in through your door and starts helping you to satisfy your girlfriend "in right way" to "put things in the right order"
Such way of thinking is a biggest mistake of western people.
Their desire to "put the things in order" or "help" is a reason of the most disasters in the Middle East and beyond. Eventually you will have to understand that it doesn't matter what the president or the prime minister are saying on the television. Western civilization isn't the only one, there are a lot of different people with own values. Like it or not, but they're sovereign subjects of international law under legitimate governments, and they haven't asked you for any kind of "help". They are capable to find out what and why they need to do.