At a guess
This is so you can be dropped into a demographic for a mailing list.
Publishers seem to love to do this.
This is sometimes used to target thier own internal mailing, and sometimes mailing lists are sold on.
But the worst offenders for selling mailing lists are Bank's, even Inland Revenue wanted to do it.
What I do is register an age of 90 (or thier highest bracket), occupation retired, income (lowest bracket, usually less thtn 15000 per year).
i have never had any spam or junk mail, not even for Polygrip.