Honestly I've always been someone who likes having multiple roleplays going on. I'm not much of a long-term roleplayer, so that's a big reason why as well. I personally have a lot of sleeping problems, so I normally reply to people around the same time because of that.
When I was younger I used to rp on Miiverse, then I switched to Quotev, then to Google+. But currently I use this, RpRepository, Roleplay.me, and emails.