They're not all that different. Actors and the "unofficial" hierarchy of nudity and sex acts.

1. mainstream actresses (tv and/or film)
2. runway model, luxury goods model (perfume, fashion, jewelry)
3. glamour model
4. stripper, softcore porn actress, OF with no sex content (hardcore or solo)
5. hardcore porn actress, OF with hardcore content

This list isn't saying one is better than the other, like saying a mainstream actress performing simulated sex with her chest showing is better than a glamour model or even a hardcore porn star. It's to say that this is how society (unofficial) views #1 in relations to other jobs that makes women strip.

Plenty of #1 do some sort of #2. Sometimes they do #3 (which includes Playboy). Some in #2 make the transition to #1. #3 can either be found in #4 or #5. It's harder for those in #5 to be either a #1 or #2, but there have been those in #1 who have switched to #5. 

What do they all have in common? Each level has plenty of women, or all, willing to shed their clothes to some degree. Only enough #2 is the most tame; it's tamer than #1 given #1 there can me either partial nudity of top half of the body, full and/or full frontal. 

There are a lot of similarities between #1, #3, #4 and #5 on what can be done in front of camera due to age and how sex scenes are setup.  When you have those in #1 supporting their past coworkers who decide to do #5 that's telling. And it ain't telling in a "aren't they so supportive, compassionate and openminded people!" sorta way.

People defend sex scenes in tv/film saying the actors feel awkward in doing them since there are cameras staring back at them, but they don't bring up the very fact that the same thing applies to porn to some degree. Porn actors also receive direction, there are cameras staring back at them, they need to show certain angles (which is "hitting your mark"), there is acting involved contrary to belief, and often times the act of performing sex when needed once the camera rolls can be tiring - just like switching on for mainstream acting once the director gives the green light. Mainstream actors will say that shooting a tv series or film isn't glamorous - well, ask a pornstar whether or not shooting a hardcore scene is glamorous. It's not.

How often times a young, unconnected aspiring actor goes to NYC or LA in hopes to become an established actor to be only shuffled into doing porn work, either soft or hardcore? I bet there are plenty. Why? Because producers and casting directors system of casting is relatively shallow: need a warm body, need to be somewhat decent looking and can read with the ability to memorize lines. 

Am I saying #1 is the same as #5? Not quite, but again they're much closer than you'd think. If anything they're the more posh identical twin of #4.

You see, tv and mainstream acting when nudity and sex scenes enter the picture are not that much difference than their more seedier cousin down the road that is porn.

Mainstream actors can get all offended that their sex scenes are being equated to softcore porn, or even hardcore porn (there have been many plenty of events where actual sex was done on set in a mainstream film), but what you see is what you get as a viewer. You can cut and put a softcore scene right next to a mainstream sex scene, so they're side by side, hit the play button and you'd be hard pressed nowadays to tell the difference. What scene would be the mainstream tv/film scene and what would be the softcore film? Sometimes you can tell due to better cinematography and lighting, but often they can make us hesitant with our confidence to differentiate.