Group roleplays are more like TTRPGs in that regard, I think. Someone usually has to take the role of the GM, and the rest make characters they roleplay in their setting. But 1x1s have a different dynamic unless one of the people wants to undertake the role of a DM/GM for the other one. I've actually seen this dynamic become more popular as of late. At least, I've been seeing more request for it. Dunno how many of those requests actually get answered.
Online roleplaying on forums like BMR is, for me, a chance to share my ideas and characters with others that might appreciate them and want to engage in collaborative storytelling. On adult sites, it's a different dynamic that I look for than on non-adult sites. Where on non-adult sites I focus completely on story building and setting and character dynamic, they shift on an adult writing site to accommodate the sexual element. When I'm on an adult site, I'm definitely looking to engage that adult element in a big way. Otherwise, I'd just be advertising on the non-adult sites that have a lot more traffic to potentially glean other writers from. On adult sites, I do a lot of 1x1 RP. On non-adult sites, I exclusively look for group RPs. I'd love to find good groups on adult sites, but the environment doesn't seem to support that kind of gathering very well. Still, I remain vigilant.
All that being said, online roleplaying is a favorite hobby of mine. I love to write. I love to worldbuild. I love to create characters and drum up plots and scenarios. And I'm also no slacker when it comes to my hobby. I go hard. "Advanced lit" by the lingo of the community. I rarely have more than one roleplay going at a time. So, all my creative effort gets poured into that one RP idea. But as full-throttle as I go into an idea, my muse veers me off track very quickly. I switch up my interest in a very capricious nature that is honestly a little frustrating. I can't focus on old notions once I get into a new idea. This goes back to my "pour all my creative effort into one RP" trait. So, I find myself cycling through ideas in a manner that often doesn't let me complete any of them. lol
In the end, online roleplaying is me hoping to write a story together with someone else that has enough shared vision of a concept with me. Then they can shoulder some of the writing and cooperatively create something that we both enjoy reading as it unfolds. Writing by myself is definitely more uniform, but the effort of doing it all myself is daunting. And it's always nice to see someone else add in notions that I didn't know I really liked!