Most people, not just men, want instant gratification. And in todays world that is easier than ever. Sure meeting someone after establishing a relationship of some sort and slowly building to a sexual relationship would be ideal for many people. But I don't think that most people these days have the actual skill set to do that.
For me, if there is someone I am interested in getting to know, I prefer to do it in person as quickly as possible. Starting the relationship online builds unrealistic expectations in the mind about how the other person is, since you can't see their facial expressions or hear their inflections and you are reading between the lines into potential sentiments that may or may not actually be there.