Because... well, because it's called Dev Ops, there's often this feeling that the philosophy excludes security... or network infrastructure... or graphics designers... or someone.
If DevOps means any one thing, it means everyone collaborating. But what it doesn't mean is someone having a veto. For example, IT Security can't swoop in and say, "there's no way we can automate the deployment of that app Because Security." That's not collaboration, it's obstructionism. What they can say is, "in order to automate the deployment of that particular app, we need to make sure x and y are happening." Security, Development, and Operations can work together to automate those requirements, helping ensure they're carried out consistently every single time. Security wins because their concerns get met as a part of the process. Development wins because they get better insight into Security concerns. Operations wins because they get to stop being the middleman who has to reconcile everyone's crap.
But this is why DevOps cannot work without management buy-in from a very high level. Like, the CEO and CIO (or CTO). The bits of your company that have traditionally worked in their own little fiefdoms need to give up their royal styles and work together. "No" is never the answer; it's "here's how." That, as I'm sure you can imagine, can be massively difficult, politically, in some organizations. And that is where people fail at DevOps.