Talk of a Step Brothers sequel has been on again and off again several times over the years, but John C. Reilly has explained fairly clearly why nothing has ever actually happened with it. While Reilly realizes just how much the comedy seems to have resonated with fans, and admits that a sequel has been something that's been discussed for years, he says that at a big part of the reason that no sequel has happened, or is currently planned to happen, is because sequels are a lot less fun for the actors then they are the fans. According to Reilly...
We've been talking about it pretty much since the first one came out. For most artists, sequels aren't the most attractive thing. Fans, of course, are different. If you like pizza, you want more pizza. I understand people really getting into the idea, but in terms of having something on the table, no, there isn't.
While there have occasionally been hints that Step Brothers 2 could happen at some point, every time John C. Reilly, Will Ferrell or director Adam McKay are asked about it, it seems to fall into the "highly unlikely" category. Will Ferrell has somewhat echoed Reilly's comments here saying that part of the reason that Step Brothers is so special a comedy is that it stands alone and that making a sequel could potentially damage that. That's not to say that real conversations haven't happened. There was even a real pitch for the story at one point, though it doesn't appear anything ever came of it.
On the one hand, you understand John C. Reilly's point that, from a creative standpoint, sequels might not be as appealing as making something new. At the same time, it's clear that a lot of actors are finding something fulfilling in sequels, as some franchises have become so big that you have actors like Robert Downey Jr. or Hugh Jackman who play the same role over and over again for more than a decade. Reilly, however, doesn't seem to be one of those people as the only sequel he's been involved in is the upcoming Ralph Breaks the Internet.
Whether or not everybody involved would be excited to make Step Brothers 2, however, is a semantic point right now, as John C. Reilly tells Indiewire that there's nothing on the table at the moment as far as a plan to make such a film. it doesn't mean it will absolutely never happen, but it certainly makes the entire thing unlikely, and while making sequels to movies decades after the original is far from uncommon these days, it feels like the longer we go without a Step Brothers 2, the less likely such a thing becomes.