Reader profile's are created by magazine companies so that they can have insight into their readers lives and interests. This allows the magazine company to understand what their readers are most interested in, meaning they can put things in their magazine which will more than likely appeal to their readers, thus selling more copies of magazines. This will then have a domino effect on the business and income of the magazine company.
Reader profiles find their data by either interviewing people on the streets and also online surveys. By stopping people on the street, you will find more detailed data and answers which could be useful as it means the company find out more about its audience, but unfortunately it is more time consuming and people who are busy or are in a rush will not stop and stand to answer questions. This is why they create online surveys. The interment is highly popular and just about everyone uses it, meaning that the company will have a better chance of receiving more answers, also the online surveys are quicker as you can read the question at your own pace, as well as answer them at your own pace too. The only downfall to the online surveys is that the audience usually don't get to answer in detail (especially if it is a closed questionnaire- yes or no answers).