I think that many of the sites have free section where you can see a lot. The websites allow us to get a little extra income to cover our travel expenses for shoots and competitions.
Speaking for myself.....
Most of my members are actually not guys who are into fitness, but guys who were intrigued by me as a person and loved my pictures. I have to cover my trips for shoots, I dont get paid for them. I also have to pay for all the outfits myself (these current shoots I have coming up..my outfits alone cost well over 2k I do sell them to other girls when I am done, but I still have to buy them, and when you have 6 shoots... you need 8 outfits a day and you cannot reuse outfits that have been published)... all of this adds up, and having the site helps. Sometimes, when I shoot exclusive content, I have to pay for the photographer, the location as well as the make-up artist.... About 4k.... so giving away everything for free does not make business sense.
There are many models on the net who have pay sites.... in the early 90s one could make excellent money.. now it is harder and to be very successfull you have to do web shows etc.. you can still do it without x rated content, but not that easily