Nude or not?

hello fellow members.ive been on this site around 8 months now and in the main i find it to be friendly and educational.there are so many talented people here producing some amazing work,which i can only admire and aspire to.however(theres always a however haha) one thing both fascinates and slightly bewilders me.having trawled through many many portfolios and posted images there seems to be a recurring theme of nudity.im sure somebody will quote statistics and contradict me,but it looks like a large percentage of models offer some kind of nude/art nude/topless/glamour/lingerie levels.and a large percentage of images posted by photographers contain the same levels.now let me say im not making judgements.i dont care who does what.but because it fascinates and bewilders me i have 2 questions.firstly for models...do you feel that in order to keep working and be able to achieve paid shoots you are obliged to shoot to these levels or do you simply do it by choice?.secondly for photographers...are these the genres that interest you the most,and do you mainly only pay models when they shoot to these levels.?im sure there are no clear demarcation lines but i wonder how many models would make money by not shooting to these levels and how many photographers would be interested if they could not shoot these levels.now please dont all get offended....as i said i am not suggesting for a second these levels are wrong and im aware its all about freedom of choice.im simply observing and its what im seeing day in day out.im also aware that there are many models and photographers producing some amazing work that do not contain these levels,but id be interested to hear what motivates people.