Ditto Roz, thank you for saying nice things about our game. It's ended now but it had a good run, and I was glad we had you when we had you. Sorry it didn't work out for you for longer.
I think your point about self-fulfilling prophecy is a good one, too. I've had players on a new game I'm running now (because oh God there are now two what is wrong with me) who, instead of asking for RP, sit around complaining about how there's nothing going on and no one wants to RP with them: this RAPIDLY becomes a self-fulfilling prophecy because when they finally do ask for RP, other players look at the history of complaints and go ehhhh maybe I don't have the energy to deal with that. Edit because I don't want people reading this and thinking I'm bitching about my current players I'M NOT the player I'm thinking of left the game already because we weren't the game for them (clearly).
I mean as a staffer I can encourage people to RP with each other in as many ways I can think of (including repeatedly abducting PCs and putting them into cages with each other and forcing them to fight like gladiators), but in the end @roz is right: people will RP with who they want to RP with.
I sympathize though, I really do. Especially on a new game I can find it very intimidating and difficult to get into RP because I'm used to playing on small games when everyone already knows who I am, so I go to a new place and have to do all this work of making RP happen for myself and I'm like, wait but ... wait. This is hard. Why is this hard? Why isn't it just falling into my lap? I almost fell off a game one of my best friends was running because it was so hard to get over myself to RP. I mean. I get super anxious sometimes and I can tell I'm being stupid but that doesn't make it less stupid when I do it.
This cuts both ways. It's a player's responsibility to put effort into finding their own story. It's a staffer's responsibility to develop a world that is encouraging to players to develop hooks with each other and with the theme. I think they're connected issues.