Well to add on to this in order to at least help. I think there are many more 18+ roleplays is because of the comfort of writing with a adult in a format like that as long as one abides to the rules but I think it is more of the idea of writing with someone with a similar mindset.

Now, from my own experience I have generally done 1x1's a lot more and posted in that format way more than the casual section.Over 50% of them never turn into RPs before my partner ghosts on me. Which is annoying and frustrating due to killing morale and group RP's are not as "driven" on smut but more on teamwork between the GM's and those who are there.