Not chooses. My mother is 57--she's become unable to learn anything new related to the computer. Some part of her brain got locked off between about 1994 and today. It's cognitive.
Whether thats true or not, thats why I said "many". I did not say what I did in a general way, as there are many circumstances which could keep a parent from learning, especially one from an earlier generation such as our mothers who grew up when PC computers were a relatively new concept (my mother is 56 and doesn't know much about computers either, but it's out of her being too busy to learn and there not being a computer she can call her own. She's otherwise eager to learn when she retires or has more freetime, and with her wits she'll quickly get the grasp of it and would be computting away in no time ^^).
Mainly, I was refering to the parents of children, teens, and just underagers in general. These parents are likely younger and are bombarded with technology all the time and many of them make extensive use of it themselves, just not computers. It is these parents, whom have access to the technology (it's in their house and they bought it), and the state of mind to be able to learn without there being such a gap in technological exposure (as it would be with an older parent) that choose not to involve themselves with their child's computer activity. Younger parents have less of an excuse, since they're statistically more likely to be making extensive use of the computer(s) themselves, whether for business, leisure, or both.
Even when thats not the case, and you have young parents who are still ignorant, then its a matter of knowing that there are dangers online and of course pornography (thats something they don't have to hear about from the computer, they hear that on tv, the radio, and in the newspapers). Even then, the parent should have enough presense of mind, dispite their ignorance of how to work a computer, to look into what their kids are doing.