The usual reply is more templates and more gates. That is often backwards.
A common request: "We have a PMO and nobody thinks it helps." The instinct is to add process, with more templates, more status reports and more gates. That usually makes it worse. These are the likelier causes, roughly in order of how often they turn out to be the real one.
It has visibility but no authority. A PMO that sees every project but cannot influence priorities, resourcing or scope is an expensive reporting function. Project managers learn that its input is optional.
It measures compliance, not outcomes. Tracking whether status reports arrive on time, rather than whether projects deliver value, rewards the wrong behavior. Everyone can tell, even if the PMO cannot.
It was built for a different portfolio. A heavy stage-gate process made for large capital projects, applied to small internal ones, creates friction out of proportion to the risk. People work around it.
It sits too low. A PMO three levels below the executives who decide resourcing can produce good analysis that never reaches anyone able to act.
Usually more than one applies, and the fix differs: more authority, different measures, a process redesigned for the real portfolio, or a new reporting line. Finding which one matters more than any generic maturity model. Adding process on top of the wrong cause only makes a PMO that people ignore easier to ignore.