Comment by cortesoft
In all my years of software development, story points never became an accurate predictor of time, even with consistent teams and process. The types of tasks we would be working on varied too much and were too novel to become predictable.
If we were working on one app and just adding features and fixing bugs, maybe it would converge to a consistent average. However, I have always worked on teams that have myriad projects, moving in and out of development, with constant support and interrupt driven work taking up a huge variable amount of time.
Management always gets frustrated when this doesn't materialize. If the instrument meant to keep management off your back doesn't do so, people will get frustrated with it.