I believe men choose Cosmo for two main reasons...

The first is that it's aimed at women and therefore must contain all the insider secrets that females share and yet won't allow men to know. It must explain what women actually want, why they behave the way they do and where the good ones hang out.

The second reason is that it makes for better wanking, as unlike lad's magazines it doesn't intersperse the semi-naked fashion models with illustrated stories of genital injuries.